Serine rich splicing factor 3 (SRSF3) plays a critical role in liver function and its loss promotes chronic liver damage and regeneration. As a consequence, genetic deletion of SRSF3 in hepatocytes caused progressive liver disease and ultimately led to hepatocellular carcinoma. Here we show that SRSF3 is decreased in human liver samples with non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), or cirrhosis that was associated with alterations in RNA splicing of known SRSF3 target genes. Hepatic SRSF3 expression was similarly decreased and RNA splicing dysregulated in mouse models of NAFLD and NASH. We showed that palmitic acid-induced oxidative stress caused conjugation of the ubiquitin like NEDD8 protein to SRSF3 and proteasome mediated degradation. SRSF3 was selectively neddylated at lysine11 and mutation of this residue (SRSF3-K11R) was sufficient to prevent both SRSF3 degradation and alterations in RNA splicing. Finally prevention of SRSF3 degradation in vivo partially protected mice from hepatic steatosis, fibrosis and inflammation. These results highlight a neddylation-dependent mechanism regulating gene expression in the liver that is disrupted in early metabolic liver disease and may contribute to the progression to NASH, cirrhosis and ultimately hepatocellular carcinoma.
Deepak Kumar, Manasi Das, Consuelo Sauceda, Lesley G. Ellies, Karina Kuo, Purva Parwal, Mehak Kaur, Lily Jih, Gautam K. Bandyopadhyay, Douglas Burton, Rohit Loomba, Olivia Osborn, Nicholas J.G. Webster
Persistent, unresolved inflammation in the liver represents a key trigger for hepatic injury and fibrosis in various liver diseases and is controlled by classically activated pro-inflammatory macrophages, while restorative macrophages of the liver are capable of reversing inflammation once the injury trigger ceases. Here we have identified a novel role for neutrophils as key contributors to resolving the inflammatory response in the liver. Using two models of liver inflammatory resolution, we found that mice undergoing neutrophil depletion during the resolution phase exhibited unresolved hepatic inflammation, activation of the fibrogenic machinery and early fibrosis. These findings were associated with an impairment of the phenotypic switch of pro-inflammatory macrophages into a restorative stage after removal of the cause of injury and an increased NLRP3 / miR-223 ratio. Mice with a deletion of the granulocyte specific miR-223 gene showed a similarly impaired resolution profile that could be reversed by restoring miR-223 levels using a miR-223 3p mimic or infusing neutrophils from wildtype animals. Collectively, our findings reveal a novel role for neutrophils in the liver as resolving effector cells that induce pro-inflammatory macrophages into a restorative phenotype, potentially via miR-223.
Carolina Jimenez Calvente, Masahiko Tameda, Casey D. Johnson, Hana del Pilar, Yun Chin Lin, Nektaria Andronikou, Xavier De Mollerat Du Jeu, Cristina Llorente, Josh Boyer, Ariel E. Feldstein
Acute liver failure (ALF) is a life-threatening condition, and liver transplantation is the only therapeutic option. Although immune dysregulation is central to its pathogenesis, the precise mechanism remains unclear. Here, we show that the number of peripheral and hepatic plasmacytoid DCs (pDCs) decrease during acute liver injury in both humans and mice. Selective depletion of pDCs in Siglechdtr/+ mice exacerbated concanavalin A–induced acute liver injury. In contrast, adoptively transferred BM-derived pDCs preferentially accumulated in the inflamed liver and protected against liver injury. This protective effect was independent of TLR7 and TLR9 signaling, since a similar effect occurred following transfer of MyD88-deficient pDCs. Alternatively, we found an unexpected immunosuppressive role of pDCs in an IL-35–dependent manner. Both Il12a and Ebi3, heterodimeric components of IL-35, were highly expressed in transferred pDCs and CD4+CD25+ Tregs. However, the protective effect of pDC transfer was completely lost in mice depleted of Tregs by anti-CD25 antibody. Moreover, pDCs derived from IL-35–deficient mice had less of a protective effect both in vivo and in vitro even in the presence of Tregs. These results highlight a unique aspect of pDCs in association with Tregs, serving as a guide for immunotherapeutic options in ALF.
Yuzo Koda, Nobuhiro Nakamoto, Po-Sung Chu, Aya Ugamura, Yohei Mikami, Toshiaki Teratani, Hanako Tsujikawa, Shunsuke Shiba, Nobuhito Taniki, Tomohisa Sujino, Kentaro Miyamoto, Takahiro Suzuki, Akihiro Yamaguchi, Rei Morikawa, Katsuaki Sato, Michiie Sakamoto, Takayuki Yoshimoto, Takanori Kanai
Ritonavir (RTV) is on the World Health Organization's List of Essential Medicines for antiretroviral therapy, but can cause hepatotoxicity by unknown mechanisms. Multiple clinical studies found that hepatotoxicity occurred in 100% of participants who were pretreated with rifampicin or efavirenz followed by RTV-containing regimens. Both rifampicin and efavirenz are activators of the pregnane X receptor (PXR), a transcription factor with significant inter-species differences in ligand-dependent activation. Using PXR-humanized mouse models, we recapitulated the RTV hepatotoxicity observed in the clinic. PXR was found to modulate RTV hepatotoxicity through CYP3A4-dependent pathways involved in RTV bioactivation, oxidative stress, and endoplasmic reticulum stress. In summary, the current work demonstrated the essential roles of human PXR and CYP3A4 in RTV hepatotoxicity, which can be applied to guide the safe use of RTV-containing regimens in the clinic.
Amina I. Shehu, Jie Lu, Pengcheng Wang, Junjie Zhu, Yue Wang, Da Yang, Deborah McMahon, Wen Xie, Frank J. Gonzalez, Xiaochao Ma
Chronic alcohol consumption causes liver injury, inflammation and fibrosis, thereby increasing morbidity and mortality. Paradoxically, modest drinking is believed to confer metabolic improvement, but the underlying mechanism remains elusive. Here, we have identified a novel hepatoprotective brain/brown adipose tissue (BAT)/liver axis. Alcohol consumption or direct alcohol administration into the brain stimulated hypothalamic neural circuits and sympathetic nerves innervating BAT, and dramatically increased BAT uncoupling protein 1 (Ucp1) expression and activity in a BAT sympathetic nerve-dependent manner. BAT and beige fat oxidized fatty acids to fuel Ucp1-mediated thermogenesis, thereby inhibiting lipid trafficking into the liver. BAT also secreted several adipokines, including adiponectin that suppressed hepatocyte injury and death. Genetic deletion of Ucp1 profoundly augmented alcohol-induced liver steatosis, injury, inflammation and fibrosis in male and female mice. Conversely, activation of BAT and beige fat through cold exposure suppressed alcoholic liver disease development. Our results unravel an unrecognized brain alcohol-sensing/sympathetic nerve/BAT/liver axis that counteracts liver steatosis and injury.
Hong Shen, Lin Jiang, Jiandie D. Lin, M. Bishr Omary, Liangyou Rui
Retinoic acid–related orphan receptor α (RORα) is considered a key regulator of polarization in liver macrophages that is closely related to nonalcoholic steatohepatitis (NASH) pathogenesis. However, hepatic microenvironments that support the function of RORα as a polarity regulator were largely unknown. Here, we identified maresin 1 (MaR1), a docosahexaenoic acid (DHA) metabolite with a function of specialized proresolving mediator, as an endogenous ligand of RORα. MaR1 enhanced the expression and transcriptional activity of RORα and thereby increased the M2 polarity of liver macrophages. Administration of MaR1 protected mice from high-fat diet–induced NASH in a RORα-dependent manner. Surprisingly, RORα increased the level of MaR1 through transcriptional induction of 12-lipoxygenase (12-LOX), a key enzyme in MaR1 biosynthesis. Furthermore, we demonstrated that modulation of 12-LOX activity enhanced the protective function of DHA against NASH. Together, these results suggest that the MaR1/RORα/12-LOX autoregulatory circuit could offer potential therapeutic strategies for curing NASH.
Yong-Hyun Han, Kyong-Oh Shin, Ju-Yeon Kim, Daulat B. Khadka, Hyeon-Ji Kim, Yong-Moon Lee, Won-Jea Cho, Ji-Young Cha, Bong-Jin Lee, Mi-Ock Lee
In contrast to microbially triggered inflammation, mechanisms promoting sterile inflammation remain poorly understood. Damage-associated molecular patterns (DAMPs) are considered key inducers of sterile inflammation following cell death, but the relative contribution of specific DAMPs, including high–mobility group box 1 (HMGB1), is ill defined. Due to the postnatal lethality of Hmgb1-knockout mice, the role of HMGB1 in sterile inflammation and disease processes in vivo remains controversial. Here, using conditional ablation strategies, we have demonstrated that epithelial, but not bone marrow–derived, HMGB1 is required for sterile inflammation following injury. Epithelial HMGB1, through its receptor RAGE, triggered recruitment of neutrophils, but not macrophages, toward necrosis. In clinically relevant models of necrosis, HMGB1/RAGE-induced neutrophil recruitment mediated subsequent amplification of injury, depending on the presence of neutrophil elastase. Notably, hepatocyte-specific HMGB1 ablation resulted in 100% survival following lethal acetaminophen intoxication. In contrast to necrosis, HMGB1 ablation did not alter inflammation or mortality in response to TNF- or FAS-mediated apoptosis. In LPS-induced shock, in which HMGB1 was considered a key mediator, HMGB1 ablation did not ameliorate inflammation or lethality, despite efficient reduction of HMGB1 serum levels. Our study establishes HMGB1 as a bona fide and targetable DAMP that selectively triggers a neutrophil-mediated injury amplification loop in the setting of necrosis.
Peter Huebener, Jean-Philippe Pradere, Celine Hernandez, Geum-Youn Gwak, Jorge Matias Caviglia, Xueru Mu, John D. Loike, Robert F. Schwabe
Innate immune activation contributes to the transition from nonalcoholic fatty liver to nonalcoholic steatohepatitis (NASH). Stimulator of IFN genes (STING, also referred to Tmem173) is a universal receptor that recognizes released DNA and triggers innate immune activation. In this work, we investigated the role of STING in the progression of NASH in mice. Both methionine- and choline-deficient diet (MCD) and high-fat diet (HFD) were used to induce NASH in mice. Strikingly, STING deficiency attenuated steatosis, fibrosis, and inflammation in livers in both murine models of NASH. Additionally, STING deficiency increased fasting glucose levels in mice independently of insulin, but mitigated HFD-induced insulin resistance and weight gain and reduced levels of cholesterol, triglycerides, and LDL in serum; it also enhanced levels of HDL. The mitochondrial DNA (mtDNA) from hepatocytes of HFD-fed mice induced TNF-α and IL-6 expression in cultured Kupffer cells (KCs), which was attenuated by STING deficiency or pretreatment with BAY11-7082 (an NF-κB inhibitor). Finally, chronic exposure to 5,6-dimethylxanthenone-4-acetic acid (DMXAA, a STING agonist) led to hepatic steatosis and inflammation in WT mice, but not in STING-deficient mice. We proposed that STING functions as an mtDNA sensor in the KCs of liver under lipid overload and induces NF-κB–dependent inflammation in NASH.
Yongsheng Yu, Yu Liu, Weishuai An, Jingwen Song, Yuefan Zhang, Xianxian Zhao
Non-alcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge signals from activated GPCRs, and modulate cell signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of Gα12 on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 level in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12 KO liver revealed that Gα12 signaling pathway regulated sirtuin 1 (SIRT1) and PPARα responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12 KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of USP22 via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12 KO mice fed high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.
Tae Hyun Kim, Yoon Mee Yang, Chang Yeob Han, Ja Hyun Koo, Hyunhee Oh, Su Sung Kim, Byoung Hoon You, Young Hee Choi, Tae-Sik Park, Chang Ho Lee, Hitoshi Kurose, Mazen Noureddin, Ekihiro Seki, Yu-Jui Yvonne Wan, Cheol Soo Choi, Sang Geon Kim
Inflammation occurs in all tissues in response to injury or stress and is the key process underlying hepatic fibrogenesis. Targeting chronic and uncontrolled inflammation is one strategy to prevent liver injury and fibrosis progression. Here, we demonstrate that triggering receptor expressed on myeloid cells-1 (TREM-1), an amplifier of inflammation, promotes liver disease by intensifying hepatic inflammation and fibrosis. In the liver, TREM-1 expression is limited to liver macrophages and monocytes and is highly upregulated on Kupffer cells, circulating monocytes, and monocyte-derived macrophages in a mouse model of chronic liver injury and fibrosis induced by carbon tetrachloride (CCl4) administration. TREM-1 signaling promotes pro-inflammatory cytokine production and mobilization of inflammatory cells to the site of injury. Deletion of Trem1 reduced liver injury, inflammatory cell infiltration, and fibrogenesis. Reconstitution of Trem1-deficient mice with Trem1-sufficient Kupffer cells restored recruitment of inflammatory monocytes and severity of liver injury. Markedly increased infiltration of liver fibrotic areas with TREM-1-positive Kupffer cells and monocytes/macrophages was found in patients with hepatic fibrosis. Our data support a role of TREM-1 in liver injury and hepatic fibrogenesis and suggests that TREM-1 is a master regulator of Kupffer cell activation, which escalates chronic liver inflammatory responses, activates hepatic stellate cells, and reveals a novel mechanism of promotion of liver fibrosis.
Anh Thu Nguyen-Lefebvre, Ashwin Ajith, Vera Portik-Dobos, Daniel David Horuzsko, Ali Syed Arbab, Amiran Dzutsev, Ramses Sadek, Giorgio Trinchieri, Anatolij Horuzsko