MLK3 promotes metabolic dysfunction induced by saturated fatty acid-enriched diet

Influence of Emulsion Lipid Droplet Crystallinity on Postprandial Endotoxin Transporters and Atherogenic And Inflammatory Profiles in Healthy Men - A Randomized Double-Blind Crossover Acute Meal Study

SCOPE

Consumption of high-fat meals is associated with increased endotoxemia, inflammation, and atherogenic profiles, with repeated postprandial responses suggested as contributors to chronically elevated risk factors. However, effects of lipid solid versus liquid state specifically have not been investigated.

METHODS AND RESULTS

This exploratory randomized crossover study tests the impact of lipid crystallinity on plasma levels of endotoxin transporters (lipopolysaccharide [LPS] binding protein [LBP] and soluble cluster of differentiation 14 [sCD14]) and select proinflammatory and atherogenic markers (tumor necrosis factor-alpha [TNF-α], C-reactive protein [CRP], interleukin-1-beta [IL-1β], interferon-gamma [IFN-γ], interleukin-6 [IL-6], soluble intercellular adhesion molecule [sICAM], soluble vascular cell adhesion molecule [sVCAM], monocyte chemoattractant protein-1 [MCP-1/CCL2], plasminogen activator inhibitor-1 [PAI-1], and fibrinogen). Fasted healthy men (n = 14, 28 ± 5.5 years, 24.1 ± 2.6 kg m-2) consumed two 50 g palm stearin oil-in-water emulsions tempered to contain either liquid or crystalline lipid droplets at 37 °C on separate occasions with blood sampling at 0, 2-, 4-, and 6-h post-meal. Timepoint data, area under the curve, and peak concentration values are compared. Overall, no treatment effects are seen (p > 0.05). There are significant effects of time, with values decreasing from baseline, for TNF-α, MCP-1/CCL2, PAI-1, and fibrinogen (p < 0.05).

CONCLUSION

Responder analysis pointed to differential treatment effects associated with some participant baseline characteristics but, overall, palm-stearin emulsion droplet crystallinity does not acutely affect plasma endotoxin transporters nor select inflammatory and atherogenic markers.

Molecular insights into the role of mixed lineage kinase 3 in cancer hallmarks

Mixed-lineage kinase 3 (MLK3) is a serine/threonine kinase of the MAPK Kinase kinase (MAP3K) family that plays critical roles in various biological processes, including cancer. Upon activation, MLK3 differentially activates downstream MAPKs, such as JNK, p38, and ERK. In addition, it regulates various non-canonical signaling pathways, such as β-catenin, AMPK, Pin1, and PAK1, to regulate cell proliferation, apoptosis, invasion, and metastasis. Recent studies have also uncovered other potentially diverse roles of MLK3 in malignancy, which include metabolic reprogramming, cancer-associated inflammation, and evasion of cancer-related immune surveillance. The role of MLK3 in cancer is complex and cancer-specific, and an understanding of its function at the molecular level aligned specifically with the cancer hallmarks will have profound therapeutic implications for diagnosing and treating MLK3-dependent cancers. This review summarizes the current knowledge about the effect of MLK3 on the hallmarks of cancer, providing insights into its potential as a promising anticancer drug target.

Integration of dietary nutrition and TRIB3 action into diabetes mellitus

Despite intensive studies for decades, the common mechanistic correlations among the underlying pathology of diabetes mellitus (DM), its complications, and effective clinical treatments remain poorly characterized. High-quality diets and nutrition therapy have played an indispensable role in the management of DM. More importantly, tribbles homolog 3 (TRIB3), a nutrient-sensing and glucose-responsive regulator, might be an important stress-regulatory switch, linking glucose homeostasis and insulin resistance. Therefore, this review aimed to introduce the latest research progress on the crosstalk between dietary nutrition intervention and TRIB3 in the development and treatment of DM. This study also summarized the possible mechanisms involved in the signaling pathways of TRIB3 action in DM, in order to gain an in-depth understanding of dietary nutrition intervention and TRIB3 in the pathogenesis of DM at the organism level.

Regulatory mechanisms of macrophage polarization in adipose tissue

In adipose tissue, macrophages are the most abundant immune cells with high heterogeneity and plasticity. Depending on environmental cues and molecular mediators, adipose tissue macrophages (ATMs) can be polarized into pro- or anti-inflammatory cells. In the state of obesity, ATMs switch from the M2 polarized state to the M1 state, which contributes to chronic inflammation, thereby promoting the pathogenic progression of obesity and other metabolic diseases. Recent studies show that multiple ATM subpopulations cluster separately from the M1 or M2 polarized state. Various factors are related to ATM polarization, including cytokines, hormones, metabolites and transcription factors. Here, we discuss our current understanding of the potential regulatory mechanisms underlying ATM polarization induced by autocrine and paracrine factors. A better understanding of how ATMs polarize may provide new therapeutic strategies for obesity-related diseases.

A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression

As a key regulator of the DNA translesion synthesis (TLS) pathway, RAD18 is error-prone and contributes to the accumulation of DNA mutations. Our previous study showed that it plays an essential role in the progression of multiple tumors. However, the mechanism through which RAD18 influences triple-negative breast cancer (TNBC), especially the interaction between tumor cells and the tumor microenvironment, remains elusive. In this study, we showed that RAD18 expression is markedly higher in patients with high T stage TNBC and inversely correlated with prognosis. High expression of RAD18 facilitated a highly stem-cell phenotype through the Hippo/YAP pathway, which supports the proliferation of TNBC. In addition, the cytokine byproduct TGF-β activates macrophages to have an M2-like tumor-associated macrophage (TAM) phenotype. Reciprocally, TGF-β from TAMs activated RAD18 in TNBC to enhance tumor stemness, forming a positive feedback loop. Inhibition of YAP or TGF-β breaks this loop and suppresses cancer stemness and proliferation In nude mice, RAD18 promoted subcutaneous transplanted tumor growth and M2-type TAM recruitment. Collectively, the RAD18-YAP-TGF-β loop is essential for the promotion of the stemness phenotype by TNBC and could be a potential therapeutic target for TNBC.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

The increased production of derivatives of molecular oxygen and nitrogen in the form of reactive oxygen species (ROS) and reactive nitrogen species (RNS) lead to molecular damage called oxidative stress. Under normal physiological conditions, the ROS generation is tightly regulated in different cells and cellular compartments. Any disturbance in the balance between the cellular generation of ROS and antioxidant balance leads to oxidative stress. In this article, we discuss the sources of ROS (endogenous and exogenous) and antioxidant mechanisms. We also focus on the pathophysiological significance of oxidative stress in various cell types of the liver. Oxidative stress is implicated in the development and progression of various liver diseases. We narrate the master regulators of ROS-mediated signaling and their contribution to liver diseases. Nonalcoholic fatty liver diseases (NAFLD) are influenced by a "multiple parallel-hit model" in which oxidative stress plays a central role. We highlight the recent findings on the role of oxidative stress in the spectrum of NAFLD, including fibrosis and liver cancer. Finally, we provide a brief overview of oxidative stress biomarkers and their therapeutic applications in various liver-related disorders. Overall, the article sheds light on the significance of oxidative stress in the pathophysiology of the liver. © 2022 American Physiological Society. Compr Physiol 12:3167-3192, 2022.

Periodontal ligament stem cells promote polarization of M2 macrophages

Macrophages are widely distributed in a variety of tissues, and the different state of macrophages polarization is closely related to the occurrence, development, and prognosis of inflammation, including periodontitis, a chronic inflammatory disease leading to tooth loss worldwide. Periodontal ligament stem cells (PDLSCs) play a key role in immune regulation and periodontal tissues regeneration, contributing to cell-based therapy of periodontitis. However, the interactions between PDLSCs and macrophages are still elusive. The purpose of present study is to investigate the effect of PDLSCs conditioned medium (PDLSCs-CM) on the macrophage polarization and the possible mechanism. PDLSCs were isolated using tissue explant methods and characterized via multipotent differentiation test and examination of expression profiles of mesenchymal stem cells (MSCs) markers. The supernatant of PDLSCs was collected, centrifuged, filtered, and used as PDLSCs-CM. Then, PDLSCs-CM was cocultured with M0 macrophages or IL-4- and IL-13-induced M2 macrophages. The level of surface markers of M1/M2 macrophages and production of several proinflammatory or anti-inflammatory factors were evaluated by flow cytometric analysis and enzyme-linked immunosorbent assay, respectively. The associated genes and proteins involved in the JNK pathway were investigated to explore the potential mechanism that may regulate PDLSCs-CM-mediated macrophage polarization. PDLSCs expressed MSCs markers, including STRO-1, CD146, CD90, and CD73, and were negative for CD34 and CD45, could undergo osteogenic and adipogenic differentiation when cultured in defined medium. After incubation with PDLSCs-CM, no significant increase of CD80+ and HLA-DR+ M1 macrophages was shown while evaluated CD209+ and CD206+ M2 macrophages were observed. In addition, the levels of anti-inflammatory factors such as IL-10, TGF-β, and CCL18 were increased instead of proinflammatory factors such as IL-1β, TNF-α with PDLSC-CM treatment. There was a decrease of JNK expression on M0 macrophages by qRT-PCR analysis and an increase of protein phosphorylation on M0 macrophages after incubation with PDLSCs-CM. Furthermore, as for the enhancement of IL-4- and IL-13-mediated M2 polarization by PDLSCs-CM, the mRNA level of JNK decreased, and the protein phosphorylation level of JNK increased. In addition, the treatment of JNK pathway inhibitor, SP600125, could inhibit the expression and secretion level of anti-inflammatory factor such as IL-10 in M2 polarization induced by PDLSCs-CM. Collectively, PDLSCs were able to induce M2 macrophage polarization instead of M1 polarization, and capable of enhancing M2 macrophage polarization induced by IL-4 and IL-13. The JNK pathway was involved in the promotion of M2 macrophage polarization.

Modulating Repolarization of Tumor-Associated Macrophages with Targeted Therapeutic Nanoparticles as a Potential Strategy for Cancer Therapy

There are always some components in the tumor microenvironment (TME), such as tumor-associated macrophages (TAMs), that help tumor cells escape the body's immune surveillance. Therefore, this situation can lead to tumor growth, progression, and metastasis, resulting in low response rates for cancer therapy. Macrophages play an important role with strong plasticity and functional diversity. Facing different microenvironmental stimulations, macrophages undergo a dynamic change in phenotype and function into two major macrophage subpopulations, namely classical activation/inflammation (M1) and alternative activation/regeneration (M2) type. Through various signaling pathways, macrophages polarize into complex groups, which can perform different immune functions. In this review, we emphasize the use of nanopreparations for macrophage related immunotherapy based on the pathological knowledge of TAMs phenotype. These macrophages targeted nanoparticles re-edit and re-educate macrophages by attenuating M2 macrophages and reducing aggregation to the TME, thereby relieving or alleviating immunosuppression. Among them, we describe in detail the cellular mechanisms and regulators of several major signaling pathways involved in the plasticity and polarization functions of macrophages. The advantages and challenges of those nanotherapeutics for these pathways have been elucidated, providing the basis and insights for the diagnosis and treatment strategies of various diseases centered on macrophages.

Loss of fragile site-associated tumor suppressor promotes antitumor immunity via macrophage polarization

Common fragile sites (CFSs) are specific breakage-prone genomic regions and are present frequently in cancer cells. The (E2-independent) E3 ubiquitin-conjugating enzyme FATS (fragile site-associated tumor suppressor) has antitumor activity in cancer cells, but the function of FATS in immune cells is unknown. Here, we report a function of FATS in tumor development via regulation of tumor immunity. Fats^-/- mice show reduced subcutaneous B16 melanoma and H7 pancreatic tumor growth compared with WT controls. The reduced tumor growth in Fats^-/- mice is macrophage dependent and is associated with a phenotypic shift of macrophages within the tumor from tumor-promoting M2-like to antitumor M1-like macrophages. In addition, FATS deficiency promotes M1 polarization by stimulating and prolonging NF-κB activation by disrupting NF-κB/IκBα negative feedback loops and indirectly enhances both CD4⁺ T helper type 1 (Th1) and cytotoxic T lymphocyte (CTL) adaptive immune responses to promote tumor regression. Notably, transfer of Fats^-/- macrophages protects mice against B16 melanoma. Together, these data suggest that FATS functions as an immune regulator and is a potential target in cancer immunotherapy.

Stress kinases in the development of liver steatosis and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is an important component of metabolic syndrome and one of the most prevalent liver diseases worldwide. This disorder is closely linked to hepatic insulin resistance, lipotoxicity, and inflammation. Although the mechanisms that cause steatosis and chronic liver injury in NAFLD remain unclear, a key component of this process is the activation of stress-activated kinases (SAPKs), including p38 and JNK in the liver and immune system. This review summarizes findings which indicate that the dysregulation of stress kinases plays a fundamental role in the development of steatosis and are important players in inducing liver fibrosis. To avoid the development of steatohepatitis and liver cancer, SAPK activity must be tightly regulated not only in the hepatocytes but also in other tissues, including cells of the immune system. Possible cellular mechanisms of SAPK actions are discussed.

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Hepatic JNK triggers steatosis and insulin resistance, decreasing lipid oxidation and ketogenesis in HFD-fed mice.

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Decreased liver expression of p38α/β in HFD increases lipogenesis.

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Hepatic p38γ/δ drive insulin resistance and inhibit autophagy, which may lead to steatosis.

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Macrophage p38α/β promote cytokine production and M1 polarization, leading to lipid accumulation in hepatocytes.

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Myeloid p38γ/δ contribute to cytokine production and neutrophil migration, protecting against steatosis, diabetes and NAFLD.

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JNK1 and p38γ induce HCC while p38α blocks it. However, deletion of hepatic JNK1/2 induces cholangiocarcinoma.

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SAPK are potential therapeutic target for metabolic disorders, steatohepatitis and liver cancer.

EB virus-induced ATR activation accelerates nasopharyngeal carcinoma growth via M2-type macrophages polarization

Chronic inflammation induced by persistent viruses infection plays an essential role in tumor progression, which influenced on the interaction between the tumor cells and the tumor microenvironment. Our earlier study showed that ATR, a key kinase participant in single-stranded DNA damage response (DDR), was obviously activated by Epstein-Barr virus (EBV) in nasopharyngeal carcinoma (NPC). However, how EBV-induced ATR activation promotes NPC by influencing inflammatory microenvironment, such as tumor-associated macrophages (TAMs), remains elusive. In this study, we showed that EBV could promote the expression of p-ATR and M2-type TAMs transformation in clinical NPC specimens. The expression of p-ATR and M2-type TAMs were closely correlated each other and involved in TNM stage, lymph node metastasis and poor prognosis of the patients. In addition, the expression levels of CD68⁺CD206⁺, Arg1, VEGF, and CCL22 were increased in EB⁺ CNE1 cells, and decreased when ATR was inhibited. In the nude mice, EBV-induced ATR activation promoted subcutaneous transplanted tumor growth, higher expression of Ki67 and lung metastasis via M2-type TAMs recruitment. Experimental data also showed that the polarization of M2, the declined tumor necrosis factor-α (TNF-α) and increased transforming growth factor-β (TGF-β) were associated with ATR. Meanwhile, ATR activation could promote PPAR-δ and inhibited c-Jun and p-JNK expression, then downregulate JNK pathway. Collectively, our current study demonstrated the EBV infection could activate the ATR pathway to accelerate the transition of TAMs to M2, suggesting ATR knockdown could be a potential effective treatment strategy for EBV-positive NPC.

Therapeutic potential of targeting mixed lineage kinases in cancer and inflammation

Dysregulation of intracellular signaling pathways is a key attribute of diseases associated with chronic inflammation, including cancer. Mitogen activated protein kinases have emerged as critical conduits of intracellular signal transmission, yet due to their ubiquitous roles in cellular processes, their direct inhibition may lead to undesired effects, thus limiting their usefulness as therapeutic targets. Mixed lineage kinases (MLKs) are mitogen-activated protein kinase kinase kinases (MAP3Ks) that interact with scaffolding proteins and function upstream of p38, JNK, ERK, and NF-kappaB to mediate diverse cellular signals. Studies involving gene silencing, genetically engineered mouse models, and small molecule inhibitors suggest that MLKs are critical in tumor progression as well as in inflammatory processes. Recent advances indicate that they may be useful targets in some types of cancer and in diseases driven by chronic inflammation including neurodegenerative diseases and metabolic diseases such as nonalcoholic steatohepatitis. This review describes existing MLK inhibitors, the roles of MLKs in various aspects of tumor progression and in the control of inflammatory processes, and the potential for therapeutic targeting of MLKs.

An immunosuppressive peptide from the horsefly inhibits inflammation by repressing macrophage maturation and phagocytosis

Ectoparasites repress host immune responses while they obtain nutrition from their hosts. Understanding the immunosuppressive mechanisms between ectoparasites and their hosts will provide new strategies to develop potential immunosuppressive drugs against immune disorder diseases. Previously, we have discovered that a small peptide, immunoregulin HA, from the horsefly (Hybomitra atriperoides) may play an immunosuppressive role in rat splenocytes. However, the targeting cells and detailed mechanisms of immunoregulin HA in immunosuppressive reactions are not well defined. Here, we show that immunoregulin HA reduces the secretion of proinflammatory cytokines upon lipopolysaccharide (LPS) stimulation. Interestingly, we discover that the major cytokines repressed by immunoregulin HA are secreted by macrophages, rather than by T cells. Furthermore, immunoregulin HA inhibits macrophage maturation and phagocytosis. Mechanically, the activations of c-JUN N-terminal kinase and extracellular signal-regulated kinase upon LPS stimulation are decreased by immunoregulin HA. Consistently, immunoregulin HA treatment exhibits an anti-inflammatory activity in a mouse model of adjuvant-induced paw inflammation. Taken together, our data reveal that immunoregulin HA conducts the anti-inflammatory activity by blocking macrophage functions.

Adapted Immune Responses of Myeloid-Derived Cells in Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is considered to be one of the most frequent chronic liver diseases worldwide and is associated with an increased risk of developing liver cirrhosis and hepatocellular carcinoma. Hepatic macrophages, mainly comprising monocyte derived macrophages and tissue resident Kupffer cells, are characterized by a high diversity and plasticity and act as key regulators during NAFLD progression, in conjunction with other infiltrating myeloid cells like neutrophils or dendritic cells. The activation and polarization of myeloid immune cells is influenced by dietary components, inflammatory signals like danger-associated molecular patterns (DAMPs) or cytokines as well as gut-derived inflammatory factors such as pathogen-associated molecular patterns (PAMPs). The functionality of myeloid leukocytes in the liver is directly linked to their inflammatory polarization, which is shaped by local and systemic inflammatory mediators such as cytokines, chemokines, PAMPs, and DAMPs. These environmental signals provoke intracellular adaptations in myeloid cells, including inflammasome and transcription factor activation, inflammatory signaling pathways, or switches in cellular metabolism. Dietary changes and obesity also promote a dysbalance in intestinal microbiota, which can facilitate intestinal permeability and bacterial translocation. The aim of this review is to highlight recent findings on the activating pathways of innate immune cells during the progression of NAFLD, dissecting local hepatic and systemic signals, dietary and metabolic factors as well as pathways of the gut-liver axis. Understanding the mechanism by which plasticity of myeloid-derived leukocytes is related to metabolic changes and NAFLD progression may provide options for new therapeutic approaches.

New insights into the role and mechanism of c-Jun-N-terminal kinase signaling in the pathobiology of liver diseases

The c-Jun-N-terminal-kinase (JNK) family is highly conserved across species such as Drosophila, C. elegans, zebrafish and mammals, and plays a central role in hepatic physiologic and pathophysiologic responses. These responses range from cell death to cell proliferation and carcinogenesis, as well as metabolism and survival, depending on the specific context and duration of activation of the JNK signaling pathway. Recently, several investigators identified the key molecules in the JNK activation loop which include apoptosis signal-regulating kinase (ASK1) and SH3-domain binding protein 5 (Sab) and their involvement in acute or chronic liver disease models. Thus, regulating JNK activation through modulating the JNK activation loop may represent an important new strategy in the prevention and treatment of acute and chronic liver diseases. In this review, we will discuss the molecular pathophysiology of the JNK activation loop and its role in the pathogenesis of liver diseases. (Hepatology 2018;67:2013-2024).

Pathophysiology of Non Alcoholic Fatty Liver Disease

The physiopathology of fatty liver and metabolic syndrome are influenced by diet, life style and inflammation, which have a major impact on the severity of the clinicopathologic outcome of non-alcoholic fatty liver disease. A short comprehensive review is provided on current knowledge of the pathophysiological interplay among major circulating effectors/mediators of fatty liver, such as circulating lipids, mediators released by adipose, muscle and liver tissues and pancreatic and gut hormones in relation to diet, exercise and inflammation.

CXCL10-Mediates Macrophage, but not Other Innate Immune Cells-Associated Inflammation in Murine Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is an inflammatory lipotoxic disorder, but how inflammatory cells are recruited and activated within the liver is still unclear. We previously reported that lipotoxic hepatocytes release CXCL10-enriched extracellular vesicles, which are potently chemotactic for cells of the innate immune system. In the present study, we sought to determine the innate immune cell involved in the inflammatory response in murine NASH and the extent to which inhibition of the chemotactic ligand CXCL10 and its cognate receptor CXCR3 could attenuate liver inflammation, injury and fibrosis. C57BL/6J CXCL10^−/−, CXCR3^−/− and wild type (WT) mice were fed chow or high saturated fat, fructose, and cholesterol (FFC) diet. FFC-fed CXCL10^−/− and WT mice displayed similar weight gain, metabolic profile, insulin resistance, and hepatic steatosis. In contrast, compared to the WT mice, FFC-fed CXCL10^−/− mice had significantly attenuated liver inflammation, injury and fibrosis. Genetic deletion of CXCL10 reduced FFC-induced proinflammatory hepatic macrophage infiltration, while natural killer cells, natural killer T cells, neutrophils and dendritic cells hepatic infiltration were not significantly affected. Our results suggest that CXCL10^−/− mice are protected against diet-induced NASH, in an obesity-independent manner. Macrophage-associated inflammation appears to be the key player in the CXCL10-mediated sterile inflammatory response in murine NASH.

Myeloid Mixed Lineage Kinase 3 Contributes to Chronic Ethanol-Induced Inflammation and Hepatocyte Injury in Mice

Proinflammatory activity of hepatic macrophages plays a key role during progression of alcoholic liver disease (ALD). Since mixed lineage kinase 3 (MLK3)-dependent phosphorylation of JNK is involved in the activation of macrophages, we tested the hypothesis that myeloid MLK3 contributes to chronic ethanol-induced inflammatory responses in liver, leading to hepatocyte injury and cell death. Primary cultures of Kupffer cells, as well in vivo chronic ethanol feeding, were used to interrogate the role of MLK3 in the progression of liver injury. Phosphorylation of MLK3 was increased in primary cultures of Kupffer cells isolated from ethanol-fed rats compared to cells from pair-fed rats. Kupffer cells from ethanol-fed rats were more sensitive to LPS-stimulated cytokine production; this sensitization was normalized by pharmacological inhibition of MLK3. Chronic ethanol feeding to mice increased MLK3 phosphorylation robustly in F4/80(+) Kupffer cells, as well as in isolated nonparenchymal cells. MLK3(-/-) mice were protected from chronic ethanol-induced phosphorylation of MLK3 and JNK, as well as multiple indicators of liver injury, including increased ALT/AST, inflammatory cytokines, and induction of RIP3. However, ethanol-induced steatosis and hepatocyte apoptosis were not affected by MLK3. Finally, chimeric mice lacking MLK3 only in myeloid cells were also protected from chronic ethanol-induced phosphorylation of JNK, expression of inflammatory cytokines, and increased ALT/AST. MLK3 expression in myeloid cells contributes to phosphorylation of JNK, increased cytokine production, and hepatocyte injury in response to chronic ethanol. Our data suggest that myeloid MLK3 could be targeted for developing potential therapeutic strategies to suppress liver injury in ALD patients.

Sab (Sh3bp5) dependence of JNK mediated inhibition of mitochondrial respiration in palmitic acid induced hepatocyte lipotoxicity

BACKGROUND & AIMS

Sustained c-Jun N-terminal kinase (JNK) activation by saturated fatty acids plays a role in lipotoxicity and the pathogenesis of non-alcoholic steatohepatitis (NASH). We have reported that the interaction of JNK with mitochondrial Sab leads to inhibition of respiration, increased reactive oxygen species (ROS), cell death and hepatotoxicity. We tested whether this pathway underlies palmitic acid (PA)-induced lipotoxicity in hepatocytes.

METHODS

Primary mouse hepatocytes (PMH) from adeno-shlacZ or adeno-shSab treated mice and HuH7 cells were used.

RESULTS

In PMH, PA dose-dependently up to 1mM stimulated oxygen consumption rate (OCR) due to mitochondrial β-oxidation. At ⩾1.5mM, PA gradually reduced OCR, followed by cell death. Inhibition of JNK, caspases or treatment with antioxidant butylated hydroxyanisole (BHA) protected PMH against cell death. Sab knockdown or a membrane permeable Sab blocking peptide prevented PA-induced mitochondrial impairment, but inhibited only the late phase of both JNK activation (beyond 4h) and cell death. In PMH, PA increased p-PERK and its downstream target CHOP, but failed to activate the IRE-1α arm of the UPR. However, Sab silencing did not affect PA-induced PERK activation. Conversely, specific inhibition of PERK prevented JNK activation and cell death, indicating a major role upstream of JNK activation.

CONCLUSIONS

The effect of p-JNK on mitochondria plays a key role in PA-mediated lipotoxicity. The interplay of p-JNK with mitochondrial Sab leads to impaired respiration, ROS production, sustained JNK activation, and apoptosis.

Immunoregulation by lipids during the development of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) represents the most common liver disorder in western countries and it is commonly associated with obesity and progression of the metabolic syndrome. Comprehending a wide spectrum of pathologic features, it is currently well recognized that a key point for the integrity of hepatocyte functionality in NAFLD is the progression from simple steatosis to non-alcoholic steatohepatitis (NASH). Indeed, activation of the innate immune system in response to hepatic metabolic stresses represents a central process that determines the evolution and the reversibility of liver damage. Despite of the burden of studies published in recent years, it is still intriguingly unclear how accumulation of lipids in hepatocytes triggers the activation of the inflammatory response leading to the recruitment of infiltrating cells of extra-hepatic origins. In this review we offer a general view on recent advances pointing out how different classes of lipids are able to specifically affect hepatocytes functionality and survival, thus differently influencing the organization of the hepatic immune response. On the other hand, we gathered recent studies intending to illustrate the basic mechanisms through which several non-parenchymal hepatic and extra-hepatic cell populations get activated in response to lipids. Finally, we indicate latter findings proposing how the immune system majorly contributes to the progression of NASH.

Macrophages and Alcohol-Related Liver Inflammation

Recent studies have suggested that macrophages have a critical role in the development of alcohol-induced inflammation in the liver. To define the precise pathogenic function of these cells during alcoholic liver disease (ALD), it is extremely important to conduct extensive studies in clinical settings that further elucidate the phenotypic diversity of macrophages In the context of ALD. Research to date already has identified several characteristics of macrophages that underlie the cells' actions, including macrophage polarization and their phenotypic diversity. Other analyses have focused on the contributions of resident versus infiltrating macrophages/monocytes, as well as on the roles of macrophage mediators, in the development of ALD. Findings point to the potential of macrophages as a therapeutic target in alcoholic liver injury. Future studies directed toward understanding how alcohol affects macrophage phenotypic switch in the liver and other tissues, whether the liver microenvironment determines macrophage function in ALO and if targeting of macrophages alleviates alcoholic liver injury, will provide promising strategies to manage patients with alcoholic hepatitis.

Regulation of Macrophage Polarization by RON Receptor Tyrosine Kinase Signaling

The M1 and M2 states of macrophage polarization are the two extremes of a physiologic/phenotypic continuum that is dynamically influenced by environmental signals. The M1/M2 paradigm is an excellent framework to understand and appreciate some of the diverse functions that macrophages perform. Molecular analysis of mouse and human macrophages indicated that they gain M1 and M2-related functions after encountering specific ligands in the tissue environment. In this perspective, I discuss the function of recepteur d’origine nantais (RON) receptor tyrosine kinase in regulating the M2-like state of macrophage activation Besides decreasing pro-inflammatory cytokine production in response to toll-like receptor-4 activation, macrophage-stimulating protein strongly suppresses nitric oxide synthase and at the same time upregulates arginase, which is the rate limiting enzyme in the ornithine biosynthesis pathway. Interestingly, RON signaling preserved some of the characteristics of the M1 state, while still promoting the hallmarks of M2 polarization. Therefore, therapeutic modulation of RON activity can shift the activation state of macrophages between acute and chronic inflammatory states.

Loss of TRB3 alters dynamics of MLK3-JNK signaling and inhibits cytokine-activated pancreatic beta cell death

Disabling cellular defense mechanisms is essential for induction of apoptosis. We have previously shown that cytokine-mediated activation of the MAP3K MLK3 stabilizes TRB3 protein levels to inhibit AKT and compromise beta cell survival. Here, we show that genetic deletion of TRB3 results in basal activation of AKT, preserves mitochondrial integrity, and confers resistance against cytokine-induced pancreatic beta cell death. Mechanistically, we find that TRB3 stabilizes MLK3, most likely by suppressing AKT-directed phosphorylation, ubiquitination, and proteasomal degradation of MLK3. Accordingly, TRB3(-/-) islets show a decrease in both the amplitude and duration of cytokine-stimulated MLK3 induction and JNK activation. It is well known that JNK signaling is facilitated by a feed forward loop of sequential kinase phosphorylation and is reinforced by a mutual stabilization of the module components. The failure of TRB3(-/-) islets to mount an optimal JNK activation response, coupled with the ability of TRB3 to engage and maintain steady state levels of MLK3, recasts TRB3 as an integral functional component of the JNK module in pancreatic beta cells.

Loss of TRB3 alters dynamics of MLK3-JNK signaling and inhibits cytokine-activated pancreatic beta cell death

Disabling cellular defense mechanisms is essential for induction of apoptosis. We have previously shown that cytokine-mediated activation of the MAP3K MLK3 stabilizes TRB3 protein levels to inhibit AKT and compromise beta cell survival. Here, we show that genetic deletion of TRB3 results in basal activation of AKT, preserves mitochondrial integrity, and confers resistance against cytokine-induced pancreatic beta cell death. Mechanistically, we find that TRB3 stabilizes MLK3, most likely by suppressing AKT-directed phosphorylation, ubiquitination, and proteasomal degradation of MLK3. Accordingly, TRB3(-/-) islets show a decrease in both the amplitude and duration of cytokine-stimulated MLK3 induction and JNK activation. It is well known that JNK signaling is facilitated by a feed forward loop of sequential kinase phosphorylation and is reinforced by a mutual stabilization of the module components. The failure of TRB3(-/-) islets to mount an optimal JNK activation response, coupled with the ability of TRB3 to engage and maintain steady state levels of MLK3, recasts TRB3 as an integral functional component of the JNK module in pancreatic beta cells.

Mixed-lineage kinase 3 deficiency promotes neointima formation through increased activation of the RhoA pathway in vascular smooth muscle cells

OBJECTIVE

Mitogen-activated protein kinase pathways play an important role in neointima formation secondary to vascular injury, in part by promoting proliferation of vascular smooth muscle cells (VSMC). Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase that activates multiple mitogen-activated protein kinase pathways and has been implicated in regulating proliferation in several cell types. However, the role of MLK3 in VSMC proliferation and neointima formation is unknown. The aim of this study was to determine the function of MLK3 in the development of neointimal hyperplasia and to elucidate the underlying mechanisms.

APPROACH AND RESULTS

Neointima formation was analyzed after endothelial denudation of carotid arteries from wild-type and MLK3-deficient mice. MLK3 deficiency promoted injury-induced neointima formation and increased proliferation of primary VSMC derived from aortas isolated from MLK3-deficient mice compared with wild-type mice. Furthermore, MLK3 deficiency increased the activation of p63Rho guanine nucleotide exchange factor, RhoA, and Rho kinase in VSMC, a pathway known to promote neointimal hyperplasia, and reconstitution of MLK3 expression attenuated Rho kinase activation. Furthermore, cJun NH2-terminal kinase activation was decreased in MLK3-deficient VSMC, and proliferation of wild-type but not MLK3 knockout cells treated with a cJun NH2-terminal kinase inhibitor was attenuated.

CONCLUSIONS

We demonstrate that MLK3 limits RhoA activation and injury-induced neointima formation by binding to and inhibiting the activation of p63Rho guanine nucleotide exchange factor, a RhoA activator. In MLK3-deficient cells, activation of p63Rho guanine nucleotide exchange factor proceeds in an unchecked manner, leading to a net increase in RhoA pathway activation. Reconstitution of MLK3 expression restores MLK3/p63Rho guanine nucleotide exchange factor interaction, which is attenuated by feedback from activated cJun NH2-terminal kinase.

The role of macrophage polarization in infectious and inflammatory diseases

Macrophages, found in circulating blood as well as integrated into several tissues and organs throughout the body, represent an important first line of defense against disease and a necessary component of healthy tissue homeostasis. Additionally, macrophages that arise from the differentiation of monocytes recruited from the blood to inflamed tissues play a central role in regulating local inflammation. Studies of macrophage activation in the last decade or so have revealed that these cells adopt a staggering range of phenotypes that are finely tuned responses to a variety of different stimuli, and that the resulting subsets of activated macrophages play critical roles in both progression and resolution of disease. This review summarizes the current understanding of the contributions of differentially polarized macrophages to various infectious and inflammatory diseases and the ongoing effort to develop novel therapies that target this key aspect of macrophage biology.

Sesame oil mitigates nutritional steatohepatitis via attenuation of oxidative stress and inflammation: a tale of two-hit hypothesis

Nonalcoholic fatty liver disease, the most common chronic liver disorder worldwide, comprises conditions from steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. NASH is associated with an increased risk of hepatocellular carcinoma. Sesame oil, a healthful food, increases resistance to oxidative stress, inflammation and protects against multiple organ injury in various animal models. We investigated the protective effect of sesame oil against nutritional steatohepatitis in mice. C57BL/6 J mice were fed with methionine-choline deficient (MCD) diet for 28 days to induce NASH. Sesame oil (1 and 2 ml/kg) was treated from 22nd to 28th day. Body weight, steatosis, triglycerides, aspartate transaminase, alanine transaminase, nitric oxide, malondialdehyde, tumor necrosis factor-α, interlukin-6, interleukin-1β, leptin, and transforming growth factor-β1 (TGF-β1) were assessed after 28 days. All tested parameters were higher in MCD-fed mice than in normal control mice. Mice fed with MCD diet for 4 weeks showed severe liver injury with steatosis, oxidative stress, and necrotic inflammation. In sesame-oil-treated mice, all tested parameters were significantly attenuated compared with MCD-alone mice. Sesame oil inhibited oxidative stress, inflammatory cytokines, leptin, and TGF-β1 in MCD-fed mice. In addition, histological analysis showed that sesame oil provided significant protection against fibrotic collagen. We conclude that sesame oil protects against steatohepatitic fibrosis by decreasing oxidative stress, inflammatory cytokines, leptin and TGF-β1.

Diet-induced obesity mediated by the JNK/DIO2 signal transduction pathway

The cJun N-terminal kinase (JNK) signaling pathway is a key mediator of metabolic stress responses caused by consuming a high-fat diet, including the development of obesity. To test the role of JNK, we examined diet-induced obesity in mice with targeted ablation of Jnk genes in the anterior pituitary gland. These mice exhibited an increase in the pituitary expression of thyroid-stimulating hormone (TSH), an increase in the blood concentration of thyroid hormone (T4), increased energy expenditure, and markedly reduced obesity compared with control mice. The increased amount of pituitary TSH was caused by reduced expression of type 2 iodothyronine deiodinase (Dio2), a gene that is required for T4-mediated negative feedback regulation of TSH expression. These data establish a molecular mechanism that accounts for the regulation of energy expenditure and the development of obesity by the JNK signaling pathway.