LUBAC Formation Is Impaired in the Livers of Mice with MCD-Dependent Nonalcoholic Steatohepatitis. Mediators Inflamm. 2015;2015:125380. [PMID: 26170532 PMCID: PMC4478366 DOI: 10.1155/2015/125380]

RNF31 alleviates liver steatosis by promoting p53/BNIP3-related mitophagy in hepatocytes

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is one of the liver illnesses that may be affected by mitophagy, which is the selective removal of damaged mitochondria. RNF31, an E3 ubiquitin ligase, is carcinogenic in many malignancies. However, the influence of RNF31 on mitochondrial homeostasis and NAFLD development remains unknown.

METHODS

Oleic-palmitic acid treated hepatocytes and high-fat diet (HFD)-fed mice were established to observe the effect of RNF31 on hepatocyte mitophagy and steatosis. Mitophagy processes were comprehensively assessed by mt-Keima fluorescence imaging, while global changes in hepatic gene expression were measured by RNA-seq.

RESULTS

The present study discovered a reduction in RNF31 expression in lipotoxic hepatocytes with mitochondrial dysfunction. The observed decrease in RNF31 expression was associated with reduced mitochondrial membrane potential, disturbed mitophagy, and increased steatosis. Additionally, the findings indicated that RNF31 is a pivotal factor in the initiation of mitophagy and the facilitation of mitochondrial homeostasis, resulting in a decrease in steatosis in lipotoxic hepatocytes. Mechanistically, RNF31 enhanced p53 ubiquitination and subsequent proteasomal degradation. Down-regulation of p53 led to increased expression of the mitophagy receptor protein BCL2 and adenovirus E1B 19 kDa-interacting protein 3 (BNIP3), thereby promoting mitophagy in hepatocytes. Furthermore, it was demonstrated that the transportation of RNF31 via small extracellular vesicles derived from mesenchymal stem cells (referred to as sEV) had a substantial influence on reducing hepatic steatosis and restoring liver function in HFD-fed mice.

CONCLUSIONS

The findings highlight RNF31's essential role in the regulation of mitochondrial homeostasis in hepatocytes, emphasizing its potential as a therapeutic target for NAFLD.

The mechanism of linear ubiquitination in regulating cell death and correlative diseases

Linear ubiquitination is a specific post-translational modification in which ubiquitin is linked through M1 residue to form multiple types of polyubiquitin chains on substrates in order to regulate cellular processes. LUBAC comprised by HOIP, HOIL-1L, and SHARPIN as a sole E3 ligase catalyzes the generation of linear ubiquitin chains, and it is simultaneously adjusted by deubiquitinases such as OTULIN and CYLD. Several studies have shown that gene mutation of linear ubiquitination in mice accompanied by different modalities of cell death would develop relative diseases. Cell death is a fundamental physiological process and responsible for embryonic development, organ maintenance, and immunity response. Therefore, it is worth speculating that linear ubiquitin mediated signaling pathway would participate in different diseases. The relative literature search was done from core collection of electronic databases such as Web of Science, PubMed, and Google Scholar using keywords about main regulators of linear ubiquitination pathway. Here, we summarize the regulatory mechanism of linear ubiquitination on cellular signaling pathway in cells with apoptosis, necroptosis, autophagy, pyroptosis, and ferroptosis. Intervening generation of linear ubiquitin chains in relative signaling pathway to regulate cell death might provide novel therapeutic insights for various human diseases.

HOIP modulates the stability of GPx4 by linear ubiquitination

LUBAC-mediated linear ubiquitination plays a pivotal role in regulation of cell death and inflammatory pathways. Genetic deficiency in LUBAC components leads to severe immune dysfunction or embryonic lethality. LUBAC has been extensively studied for its role in mediating TNF signaling. However, Tnfr1 knockout is not able to fully rescue the embryonic lethality of LUBAC deficiency, suggesting that LUBAC may modify additional key cellular substrates in promoting cell survival. GPx4 is an important selenoprotein involved in regulating cellular redox homeostasis in defense against lipid peroxidation-mediated cell death known as ferroptosis. Here we demonstrate that LUBAC deficiency sensitizes to ferroptosis by promoting GPx4 degradation and downstream lipid peroxidation. LUBAC binds and stabilizes GPx4 by modulating its linear ubiquitination both in normal condition and under oxidative stress. Our findings identify GPx4 as a key substrate of LUBAC and a previously unrecognized role of LUBAC-mediated linear ubiquitination in regulating cellular redox status and cell death.

Met1-linked ubiquitin signalling in health and disease: inflammation, immunity, cancer, and beyond

Post-translational modification of proteins with ubiquitin (ubiquitination) provides a rapid and versatile mechanism for regulating cellular signalling systems. Met1-linked (or 'linear') ubiquitin chains have emerged as a key regulatory signal that controls cell death, immune signalling, and other vital cellular functions. The molecular machinery that assembles, senses, and disassembles Met1-linked ubiquitin chains is highly specific. In recent years, the thorough biochemical and genetic characterisation of the enzymes and proteins of the Met1-linked ubiquitin signalling machinery has paved the way for substantial advances in our understanding of how Met1-linked ubiquitin chains control cell signalling and biology. Here, we review current knowledge and recent insights into the role of Met1-linked ubiquitin chains in cell signalling with an emphasis on their role in disease biology. Met1-linked ubiquitin has potent regulatory functions in immune signalling, NF-κB transcription factor activation, and cell death. Importantly, mounting evidence shows that dysregulation of Met1-linked ubiquitin signalling is associated with multiple human diseases, including immune disorders, cancer, and neurodegeneration. We discuss the latest evidence on the cellular function of Met1-linked ubiquitin in the context of its associated diseases and highlight new emerging roles of Met1-linked ubiquitin chains in cell signalling, including regulation of protein quality control and metabolism.

Keratinocyte-specific deletion of SHARPIN induces atopic dermatitis-like inflammation in mice

Spontaneous mutations in the SHANK-associated RH domain interacting protein (Sharpin) resulted in a severe autoinflammatory type of chronic proliferative dermatitis, inflammation in other organs, and lymphoid organ defects. To determine whether cell-type restricted loss of Sharpin causes similar lesions, a conditional null mutant was created. Ubiquitously expressing cre-recombinase recapitulated the phenotype seen in spontaneous mutant mice. Limiting expression to keratinocytes (using a Krt14-cre) induced a chronic eosinophilic dermatitis, but no inflammation in other organs or lymphoid organ defects. The dermatitis was associated with a markedly increased concentration of serum IgE and IL18. Crosses with S100a4-cre resulted in milder skin lesions and moderate to severe arthritis. This conditional null mutant will enable more detailed studies on the role of SHARPIN in regulating NFkB and inflammation, while the Krt14-Sharpin-/- provides a new model to study atopic dermatitis.

Shank-associated RH domain interactor signaling in tumorigenesis

Shank-associated RH domain interactor (SHARPIN) is a component of the linear ubiquitin chain activation complex, which is essential for p53 signaling and inflammation. Previous studies have demonstrated that SHARPIN functions in tumor cell survival, growth, invasion and tumorigenesis. These functions include the regulation of p53 proteins via poly-ubiquitination, interaction with a type II protein arginine methyltransferase 5 in melanoma cells, modulating ras-associated protein-1 through p38 and c-Jun N-terminal kinases/c-Jun signaling, and mediating phosphoinositide 3-kinase/AKT signaling via phosphatase and tensin homologue deleted on chromosome 10. Hence, SHARPIN not only participates in the inflammatory response but also serves a critical role in tumor cells. The present review summarizes the biological functions of the absence or presence of SHARPIN with regard to activating the canonical NF-κB signaling pathway and the effects on p53 and other signaling pathways for the modulation of tumorigenesis. Therefore, this review provides insight into the underlying role and mechanisms of SHARPIN in tumorigenesis, as well as its potential application in cancer therapy.

Additional Candida albicans administration enhances the severity of dextran sulfate solution induced colitis mouse model through leaky gut-enhanced systemic inflammation and gut-dysbiosis but attenuated by Lactobacillus rhamnosus L34

is abundant in the human gut mycobiota but this species does not colonize the mouse gastrointestinal tract. C. albicans administration in dextran-sulfate solution (DSS) induced-colitis mouse model (DSS+Candida) might resemble more to human condition, therefore, a DSS colitis model with Candida administration was studied; first, to test the influence of fungi in DSS model and second, to test the efficacy of Lactobacillus rhamnosus L34. We demonstrated serum (1→3)-β-D-glucan (BG) elevation in patients with IBD and endoscopic moderate colitis in clinical remission, supporting the possible influence of gut fungi toward IBD in human. Then, in mouse model, Candida gavage was found to worsen the DSS model indicated by higher mortality rate, more severe colon histology and enhanced gut-leakage (FITC-dextran assay, endotoxemia, serum BG and blood bacterial burdens) but did not affect weight loss and diarrhea. DSS+Candida induced higher pro-inflammatory cytokines both in blood and in intestinal tissue. Worsened systemic pro-inflammatory cytokine responses in DSS+Candida compared with DSS alone was possibly due to the more severe translocation of LPS, BG and bacteria (not fungemia) from gut into systemic circulation. Interestingly, bacteremia from Pseudomonas aeruginosa was more frequently isolated from DSS+Candida than DSS alone. In parallel, P. aeruginosa was also isolated from fecal culture in most of the mice in DSS+Candida group supported by prominent Gammaproteobacteria in fecal microbioata analysis. However, L. rhamnosus L34 attenuated both DSS+Candida and DSS model through the attenuation of gut local inflammation (cytokines and histology), gut-leakage severity, fecal dysbiosis (culture method and microbiome analysis) and systemic inflammation (serum cytokines). In conclusion, gut Candida in DSS model induced fecal bacterial dysbiosis and enhanced leaky-gut induced bacteremia. Probiotic treatment strategy aiming to reduce gut-fungi and fecal dysbiosis could attenuate disease severity. Investigation on gut fungi in patients with IBD is highly interesting.

Effects of probiotic administration on immune responses of children and adolescents with type 1 diabetes to a quadrivalent inactivated influenza vaccine

This study was planned to evaluate whether a 3-month treatment with Lactobacillus rhamnosus GG (LGG) can modify immune system functions in children and adolescents with type 1 diabetes (T1D), leading to an increased immune response to an injectable quadrivalent inactivated influenza vaccine (QIV). A total of 87 pediatric patients with T1D were screened, although 34 patients in the Probiotic group and 30 in the Control group accepted to be vaccinated with QIV and completed the study. Vaccine immunogenicity and safety and the inflammatory cytokine response were studied. Results showed that QIV was immunogenic and safe in T1D pediatric patients and pre-administration of LGG for three months did not substantially modify the QIV humoral immunity. The combination of QIV and LGG reduced inflammatory responses (i.e., IFN-γ, IL17A, IL-17F, IL-6, and TNF-α) from activated PBMCs of pediatric patients with T1D, without dampening the production of seroprotective antibodies. In conclusion, QIV is associated with an adequate immunogenicity in children and adolescents with T1D in presence of a good safety profile. Although a systematic administration of LGG did not result in an improvement of humoral responses to an influenza vaccine, the probiotic did induce important anti-inflammatory effects.

Neutrophil Cathepsin G and Tumor Cell RAGE Facilitate Neutrophil Anti-Tumor Cytotoxicity

Neutrophils are a heterogeneous population of myeloid cells which may either promote or hinder tumor growth and progression. Anti-tumor neutrophils have the capacity to kill tumor cells in a contact-dependent manner. However, the molecular mechanisms underlying tumor cell recognition by neutrophils remained unexplored. Tumor cells were shown to express aberrant glycosylation patterns and neutrophils are equipped with receptors capable of recognizing such glycosylations. Accordingly, we hypothesized that the receptor for advanced glycation end products (RAGE) may facilitate neutrophil recognition of tumor cells. Indeed, RAGE decoy receptors and RAGE-specific blocking antibodies dramatically reduce tumor cell susceptibility to neutrophil cytotoxicity. Unexpectedly, we found that tumor cell RAGE rather than neutrophil RAGE is important for the killing process. We further identified neutrophil Cathepsin G as the neutrophil component interacting with tumor cell RAGE. Cathepsin G-deficient neutrophils show impaired ability to kill tumor cells, suggesting that RAGE-Cathepsin G interaction is required for neutrophil cytotoxicity. These data unravel new aspects of neutrophil anti-tumor activity and identify a novel role for RAGE and Cathepsin G in neutrophil-mediated cytotoxicity.

TIMP-1 Mediates Inflammatory and Immune Response to IL-6 in Adult Orbital Xanthogranulomatous Disease

Purpose: To explore the pathogenesis that TIMP-1 mediated in adult orbital xanthogranulomatous disease (AOXGD), a rare type of non-Langerhans histiocytosis that damages the appearance and quality of life of patientsMethods: We reviewed 22 patients diagnosed with AOXGD based on clinical manifestations and histological analysis, and then investigated the expression of TIMP-1 and IL-6 with q-PCR and IHC in AOXGD tissues and the possible mechanism involved in the induction of TIMP-1 by IL-6.Results: IL-6 and TIMP-1 were significantly increased in AOXGD tissues. IL-6 promoted TIMP-1 production by M1 macrophages by stimulating the phosphorylation of JAK2 and STAT3. Moreover, IL-17 and IFN-γ, the classical markers of Th1 and Th17 cells, were increased in AOXGD.Conclusion: These data implied that the IL6~JAK2/STAT3-TIMP-1 signalling pathway is activated in AOXGD and that adaptive Th1 and Th17 responses are involved in the development of AOXGD.

The bacterial siderophore enterobactin confers survival advantage to Salmonella in macrophages

Enterobactin (Ent), a prototypical bacterial siderophore known for its unparalleled affinity for iron, is widely conserved among members of the Enterobacteriaceae family of Gram-negative bacteria. In this study, we demonstrated that, aside from mediating iron acquisition, Ent also dampened the macrophages (MΦs) antimicrobial responses against intracellular infection by Salmonella enterica serovar Typhimurium. Accordingly, the loss of Ent expression (ΔentB) in Salmonella demoted their survivability against MΦs. Addition of exogenous Ent not only rescued the survival of ΔentB Salmonella, but also augmented WT Salmonella to better withstand the microbicidal activity of MΦs. The protection conferred to WT Salmonella was observed only when Ent was administered as iron-free, thus indicating the requirement of iron chelation in this context. In contrast, the exogenous iron-bound Ent retained its ability to promote the survival of ΔentB Salmonella, albeit modestly. Assessment on MΦs labile iron pool (LIP) revealed that iron-free Ent is able to permeate into MΦs, chelate the intracellular LIP, and regulate the expression of several key iron-regulatory proteins, i.e., divalent metal transporter 1, ferroportin, and hepcidin. Chelation of iron by Ent was also observed to promote the MΦs towards M2 polarization. Collectively, our findings demonstrated that Ent not only facilitates bacterial iron uptake but also disrupts MΦs iron homeostasis and M1/M2 polarization to safeguard intracellular bacteria against the anti-bacterial effects of their host.

Interleukin-22, a potent target for treatment of non-autoimmune diseases

Interleukin -22 (IL-22) is a member of interleukin-10 (IL-10) family cytokines that is produced by different types of lymphocytes included in both innate and adaptive immune systems. These lymphocytes include activated T cells, most notably Th17 and Th22 cells, as well as NK cells, γδ T cells, etc. IL-22 mediate its effects via the IL-22-IL-22R complex and subsequent Janus Kinase-signal transduces and activators transcription (JAK-STAT) signaling pathway. According to recent evidence, IL-22 played a critical role in the pathogenesis of many non-autoimmune diseases. In this review, we mainly discussed the recent findings and advancements of the role of IL-22 in several non-autoimmune diseases, such as acute lung injury, atherosclerosis and some bacterial infections, suggesting that IL-22 may have therapeutic potential for treating non-autoimmune diseases.

The Presence of Uveitis Is Associated with a Sustained Response to the Interleukin (IL)-1 Inhibitors Anakinra and Canakinumab in Behçet's Disease

Purpose: To identify factors associated with sustained response to interleukin (IL)-1 inhibition among demographic, clinical and therapeutic data in patients with Behçet disease (BD).Methods: BD patients treated with anakinra or canakinumab were enrolled. Patients were divided into two groups according to the clinical response: group 1 included subjects showing a treatment duration of at least 52 weeks and no secondary inefficacy during the first follow-up year; the remaining patients were included in the group 2. Demographic, clinical and therapeutic data were analyzed to identify significant differences between groups.Results: Eighteen patients were included in group 1 and 18 patients in group 2. A better response to IL-1 inhibitors was significantly more common among patients with BD-related uveitis (p = 0.006) and patients with a longer disease duration (p = 0.03).Conclusion: IL-1 blockade is effective in BD, especially in the subset of patients presenting eye involvement and in those with long-lasting disease.

Apoptosis and non-alcoholic fatty liver diseases

The number of patients with nonalcoholic fatty liver diseases (NAFLD) including nonalcoholic steatohepatitis (NASH), has been increasing. NASH causes cirrhosis and hepatocellular carcinoma (HCC) and is one of the most serious health problems in the world. The mechanism through which NASH progresses is still largely unknown. Activation of caspases, Bcl-2 family proteins, and c-Jun N-terminal kinase-induced hepatocyte apoptosis plays a role in the activation of NAFLD/NASH. Apoptotic hepatocytes stimulate immune cells and hepatic stellate cells toward the progression of fibrosis in the liver through the production of inflammasomes and cytokines. Abnormalities in glucose and lipid metabolism as well as microbiota accelerate these processes. The production of reactive oxygen species, oxidative stress, and endoplasmic reticulum stress is also involved. Cell death, including apoptosis, seems very important in the progression of NAFLD and NASH. Recently, inhibitors of apoptosis have been developed as drugs for the treatment of NASH and may prevent cirrhosis and HCC. Increased hepatocyte apoptosis may distinguish NASH from NAFLD, and the improvement of apoptosis could play a role in controlling the development of NASH. In this review, the association between apoptosis and NAFLD/NASH are discussed. This review could provide their knowledge, which plays a role in seeing the patients with NAFLD/NASH in daily clinical practice.

Updates on Dietary Models of Nonalcoholic Fatty Liver Disease: Current Studies and Insights

Nonalcoholic fatty liver disease (NAFLD) is a disease of increasing interest, as its prevalence is on the rise. NAFLD has been linked to metabolic syndrome, which is becoming more common due to the Western diet. Because NAFLD can lead to cirrhosis and related complications including hepatocellular carcinoma, the increasing prevalence is concerning, and medical therapy aimed at treating NAFLD is of great interest. Researchers studying the effects of medical therapy on NAFLD use dietary mouse models. The two main types of mouse model diets are the methionine- and choline-deficient (MCD) diet and the Western-like diet (WD). Although both induce NAFLD, the mechanisms are very different. We reviewed several studies conducted within the last 5 years that used MCD diet or WD mouse models in order to mimic this disease in a way most similar to humans. The MCD diet inconsistently induces NAFLD and fibrosis and does not completely induce metabolic syndrome. Thus, the clinical significance of the MCD diet is questionable. In contrast, WD mouse models consisting of high fat, cholesterol, and a combination of high-fructose corn syrup, sucrose, fructose, or glucose not only lead to metabolic syndrome but also induce NAFLD with fibrosis, making these choices most suitable for research.

Reduced SHARPIN and LUBAC Formation May Contribute to CCl₄- or Acetaminophen-Induced Liver Cirrhosis in Mice

Linear ubiquitin chain assembly complex (LUBAC), composed of SHARPIN (SHANK-associated RH domain-interacting protein), HOIL-1L (longer isoform of heme-oxidized iron-regulatory protein 2 ubiquitin ligase-1), and HOIP (HOIL-1L interacting protein), forms linear ubiquitin on nuclear factor-κB (NF-κB) essential modulator (NEMO) and induces NF-κB pathway activation. SHARPIN expression and LUBAC formation were significantly reduced in the livers of mice 24 h after the injection of either carbon tetrachloride (CCl₄) or acetaminophen (APAP), both of which produced the fulminant hepatitis phenotype. To elucidate its pathological significance, hepatic SHARPIN expression was suppressed in mice by injecting shRNA adenovirus via the tail vein. Seven days after this transduction, without additional inflammatory stimuli, substantial inflammation and fibrosis with enhanced hepatocyte apoptosis occurred in the livers. A similar but more severe phenotype was observed with suppression of HOIP, which is responsible for the E3 ligase activity of LUBAC. Furthermore, in good agreement with these in vivo results, transduction of Hepa1-6 hepatoma cells with SHARPIN, HOIL-1L, or HOIP shRNA adenovirus induced apoptosis of these cells in response to tumor necrosis factor-α (TNFα) stimulation. Thus, LUBAC is essential for the survival of hepatocytes, and it is likely that reduction of LUBAC is a factor promoting hepatocyte death in addition to the direct effect of drug toxicity.

Contribution of Mass Spectrometry-Based Proteomics to the Understanding of TNF-α Signaling

NF-κB is a family of ubiquitous dimeric transcription factors that play a role in a myriad of cellular processes, ranging from differentiation to stress response and immunity. In inflammation, activation of NF-κB is mediated by pro-inflammatory cytokines, in particular the prototypic cytokines IL-1β and TNF-α, which trigger the activation of complex signaling cascades. In spite of decades of research, the system level understanding of TNF-α signaling is still incomplete. This is partially due to the limited knowledge at the proteome level. The objective of this review is to summarize and critically evaluate the current status of the proteomic research on TNF-α signaling. We will discuss the merits and flaws of the existing studies as well as the insights that they have generated into the proteomic landscape and architecture connected to this signaling pathway. Besides delineating past and current trends in TNF-α proteomic research, we will identify research directions and new methodologies that can further contribute to characterize the TNF-α associated proteome in space and time.

Present and future of biologic drugs in primary Sjögren's syndrome

INTRODUCTION

Primary Sjögren's (pSS) syndrome is a chronic, autoimmune, and systemic disease characterized by xerostomia, xerophthalmia, muscle pain and fatigue. The disease may be complicated by a systemic involvement, such as a pulmonary fibrosis or the development of lymphoma which severely worsens the prognosis. Actually, there are no recommendations for the management of pSS. However, recent advances in the understanding of its pathogenesis have uncovered some pathways that have potential as therapeutic targets. Areas covered: In this review, the authors present the biologic drugs potentially valuable to the treatment of pSS in light of its physiopathology with a 'bird's eye' view of future prospects. The authors took into account relevant studies published from 2004 to 2016. Expert opinion: Biological treatment in pSS is a promising opportunity to potentially control disease activity and prevent its complication. Currently, inhibition of B-cell and IL-17 pathways seem to be the most promising avenues. New achievements in the knowledge of pSS pathophysiology are necessary in order to try to simultaneously predict the predominant pathogenic pathway, the kind of patients at major risk to develop a more severe disease, and the appropriate biological therapy to use.