Hepatic stellate cells (HSCs) play critical roles in liver fibrosis and hepatocellular carcinoma (HCC). Vitamin D receptor (VDR) activation in HSCs inhibits liver inflammation and fibrosis. We found ...that p62/SQSTM1, a protein upregulated in liver parenchymal cells but downregulated in HCC-associated HSCs, negatively controls HSC activation. Total body or HSC-specific p62 ablation potentiates HSCs and enhances inflammation, fibrosis, and HCC progression. p62 directly interacts with VDR and RXR promoting their heterodimerization, which is critical for VDR:RXR target gene recruitment. Loss of p62 in HSCs impairs the repression of fibrosis and inflammation by VDR agonists. This demonstrates that p62 is a negative regulator of liver inflammation and fibrosis through its ability to promote VDR signaling in HSCs, whose activation supports HCC.
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•p62 levels are reduced in hepatic stellate cells (HSCs) in human HCC samples•Loss of p62 in HSCs results in increased fibrosis, inflammation, and HCC•p62 is critical for VDR:RXR heterodimerization and inhibition of HSC activation•Enhanced HSC activation by p62 loss impairs VDR signaling and promotes HCC
In hepatocellular carcinoma (HCC), p62 is increased in hepatocytes but decreased in hepatic stellate cells (HSCs). Duran et al. show that loss of p62 in HSCs promotes HCC development by reducing the vitamin D receptor (VDR)-RXR interaction, leading to impaired repression of fibrosis and inflammation by VDR.
The c-Jun NH(2)-terminal kinase (JNK) is a critical determinant of obesity-associated inflammation and glucose intolerance. The upstream mechanisms controlling this pathway are still unknown. Here we ...report that the levels of the PB1 domain-containing adaptor NBR1 correlated with the expression of proinflammatory molecules in adipose tissue from human patients with metabolic syndrome, suggesting that NBR1 plays a key role in adipose-tissue inflammation. We also show that NBR1 inactivation in the myeloid compartment impairs the function, M1 polarization, and chemotactic activity of macrophages; prevents inflammation of adipose tissue; and improves glucose tolerance in obese mice. Furthermore, we demonstrate that an interaction between the PB1 domains of NBR1 and the mitogen-activated kinase kinase 3 (MEKK3) enables the formation of a signaling complex required for the activation of JNK. Together, these discoveries identify an NBR1-MEKK3 complex as a key regulator of JNK signaling and adipose tissue inflammation in obesity.
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•NBR1 positively correlates with adipose inflammation in human obese patients•NBR1 is increased in adipose tissue macrophages in obese mice•Myeloid-specific NBR1−/− mice display reduced obesity-induced insulin resistance•The NBR1-MEKK3 complex is important in JNK activation in macrophages
The inflammatory kinase JNK is a critical determinant of obesity-associated inflammation and glucose intolerance. Hernadez et al. identify the macrophage NBR1-MEKK3 complex as a key upstream regulator of JNK signaling.
Farnesoid X receptor (FXR) agonism is emerging as an important potential therapeutic mechanism of action for multiple chronic liver diseases. The bile acid‐derived FXR agonist obeticholic acid (OCA) ...has shown promise in a phase 2 study in patients with nonalcoholic steatohepatitis (NASH). Here, we report efficacy of the novel nonbile acid FXR agonist tropifexor (LJN452) in two distinct preclinical models of NASH. The efficacy of tropifexor at <1 mg/kg doses was superior to that of OCA at 25 mg/kg in the liver in both NASH models. In a chemical and dietary model of NASH (Stelic animal model STAM), tropifexor reversed established fibrosis and reduced the nonalcoholic fatty liver disease activity score and hepatic triglycerides. In an insulin‐resistant obese NASH model (amylin liver NASH model AMLN), tropifexor markedly reduced steatohepatitis, fibrosis, and profibrogenic gene expression. Transcriptome analysis of livers from AMLN mice revealed 461 differentially expressed genes following tropifexor treatment that included a combination of signatures associated with reduction of oxidative stress, fibrogenesis, and inflammation. Conclusion: Based on preclinical validation in animal models, tropifexor is a promising investigational therapy that is currently under phase 2 development for NASH.
Farnesoid X receptor (FXR) agonists are emerging as important potential therapeutics for the treatment of nonalcoholic steatohepatitis (NASH) patients, as they exert positive effects on multiple ...aspects of the disease. FXR agonists reduce lipid accumulation in the liver, hepatocellular inflammation, hepatic injury, and fibrosis. While there are currently no approved therapies for NASH, the bile acid-derived FXR agonist obeticholic acid (OCA; 6-ethyl chenodeoxycholic acid) has shown promise in clinical studies. Previously, we described the discovery of tropifexor (LJN452), the most potent non-bile acid FXR agonist currently in clinical investigation. Here, we report the discovery of a novel chemical series of non-bile acid FXR agonists based on a tricyclic dihydrochromenopyrazole core from which emerged nidufexor (LMB763), a compound with partial FXR agonistic activity in vitro and FXR-dependent gene modulation in vivo. Nidufexor has advanced to Phase 2 human clinical trials in patients with NASH and diabetic nephropathy.
Eukaryotic PFK (phosphofructokinase), a key regulatory enzyme in glycolysis, has homologous N- and C-terminal domains thought to result from duplication, fusion and divergence of an ancestral ...prokaryotic gene. It has been suggested that both the active site and the Fru-2,6-P2 (fructose 2,6-bisphosphate) allosteric site are formed by opposing N- and C-termini of subunits orientated antiparallel in a dimer. In contrast, we show in the present study that in fact the N-terminal halves form the active site, since expression of the N-terminal half of the enzymes from Dictyostelium discoideum and human muscle in PFK-deficient yeast restored growth on glucose. However, the N-terminus alone was not stable in vitro. The C-terminus is not catalytic, but is needed for stability of the enzyme, as is the connecting peptide that normally joins the two domains (here included in the N-terminus). Co-expression of homologous, but not heterologous, N- and C-termini yielded stable fully active enzymes in vitro with sizes and kinetic properties similar to those of the wild-type tetrameric enzymes. This indicates that the separately translated domains can fold sufficiently well to bind to each other, that such binding of complementary domains is stable and that the alignment is sufficiently accurate and tight as to preserve metabolite binding sites and allosteric interactions.
Mammalian phosphofructokinase originated by duplication, fusion, and divergence of a primitive prokaryotic gene, with the duplicated fructose 6-phosphate catalytic site in the C-terminal half ...becoming an allosteric site for the activator fructose 2,6-bisphosphate. It has been suggested that both sites are shared across the interface between subunits aligned in an antiparallel orientation, the N-terminal half of one subunit facing the C-terminal half of the other. The composition of these binding sites and the way in which subunits interact to form the dimer within the tetrameric enzyme have been reexamined by systematic point mutations to alanine of key amino acid residues of human muscle phosphofructokinase. We found that residues His-199, His-298, Arg-201, and Arg-292 contribute to the catalytic site and not to the allosteric site, because their mutation decreased the affinity for fructose 6-phosphate without affecting the activation by fructose 2,6-bisphosphate or its binding affinity. In contrast, residues Arg-566, Arg-655, and His-661 were critical components of the fructose bisphosphate allosteric site, because their mutation strongly reduced the action and affinity of the activator, with no alteration of substrate binding to the active site. Our results suggest that mammalian phosphofructokinase subunits associate with the N-terminal halves facing each other to form the two catalytic sites/dimer and the C-terminal halves forming the allosteric sites. Additionally, mutation of certain residues eliminated activation by fructose 1,6-bisphosphate, but not its binding, with little effect on activation by fructose 2,6-bisphosphate, indicating a divergence in the signal transduction route despite their binding to the same site.
Mammalian phosphofructokinase originated by duplication, fusion, and
divergence of a primitive prokaryotic gene, with the duplicated fructose
6-phosphate catalytic site in the C-terminal half ...becoming an allosteric site
for the activator fructose 2,6-bisphosphate. It has been suggested that both
sites are shared across the interface between subunits aligned in an
antiparallel orientation, the N-terminal half of one subunit facing the
C-terminal half of the other. The composition of these binding sites and the
way in which subunits interact to form the dimer within the tetrameric enzyme
have been reexamined by systematic point mutations to alanine of key amino
acid residues of human muscle phosphofructokinase. We found that residues
His-199, His-298, Arg-201, and Arg-292 contribute to the catalytic site and
not to the allosteric site, because their mutation decreased the affinity for
fructose 6-phosphate without affecting the activation by fructose
2,6-bisphosphate or its binding affinity. In contrast, residues Arg-566,
Arg-655, and His-661 were critical components of the fructose bisphosphate
allosteric site, because their mutation strongly reduced the action and
affinity of the activator, with no alteration of substrate binding to the
active site. Our results suggest that mammalian phosphofructokinase subunits
associate with the N-terminal halves facing each other to form the two
catalytic sites/dimer and the C-terminal halves forming the allosteric sites.
Additionally, mutation of certain residues eliminated activation by fructose
1,6-bisphosphate, but not its binding, with little effect on activation by
fructose 2,6-bisphosphate, indicating a divergence in the signal transduction
route despite their binding to the same site.
This paper introducesCollage, a high-level IMS-LD compliant authoring tool that is specialized for CSCL (Computer-Supported collaborative Learning). Nowadays CSCL is a key trend in e-learning since ...it highlights the importance of social interactions as an essential element of learning. CSCL is an interdisciplinary domain, which demands participatory design techniques that allow teachers to get directly involved in design activities. Developing CSCL designs using LD is a difficult task for teachers since LD is a complex technical specification and modelling collaborative characteristics can be tricky.Collagehelps teachers in the process of creating their own potentially effective collaborative Learning Designs by reusing and customizing patterns, according to the requirements of a particular learning situation. These patterns, called collaborative Learning Flow Patterns (CLFPs), represent best practices that are repetitively used by practitioners when structuring the flow of (collaborative) learning activities. An example of an LD that can be created usingCollageis illustrated in the paper. Preliminary evaluation results show that teachers with experience in CL but without LD knowledge, can successfully design real collaborative learning experiences usingCollage.
Current research work in e-learning and more specifically in the field of CSCL (Computer Supported Collaborative Learning) deals with design of collaborative activities, according to ...computer-interpretable specifications, such as IMS Learning Design, and their posterior enactment using LMSs (Learning Management Systems). A script that describes such collaborative activities is typically designed beforehand in order to structure collaboration, and defines the features that determine the behavior of the LMS, for instance, the sequence of activities or the groups/role distribution. In CSCL settings, group management and composition are especially relevant and affect the chances of achieving the expected learning outcomes. This paper presents a software tool, namedInstanceCollage, which aims at facilitating the configuration and population of groups for IMS-LD scripts created with the authoring toolCollage, and discusses the implications of the IMS-LD specification with respect to this task. InstanceCollage is designed to process collaboration scripts based on CLFPs (Collaborative Learning Flow Patterns). Using this type of patterns,InstanceCollagefocuses on the importance of understanding the function of groups within the learning strategy of the script. This paper describes the approach taken inInstanceCollageto facilitate this understanding for non-expert users. Additionally, two case studies are presented, which represent complex authentic collaborative learning scenarios, as a proof of concept of the functionality of this tool. The case studies are also used to illustrate the requirements of group configuration tools and to show that InstanceCollage complies to such requirements.
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