p38 alpha MAPK inhibits JNK activation and collaborates with IkappaB kinase 2 to prevent endotoxin-induced liver failure. EMBO Rep. 2008;9:1048-1054. [PMID: 18704119 DOI: 10.1038/embor.2008.149]

A combination of alveolar type 2-specific p38α activation with a high-fat diet increases inflammatory markers in mouse lungs

Chronic respiratory diseases such as asthma and chronic obstructive pulmonary disease afflict millions of individuals globally and are significant sources of disease mortality. While the molecular mechanisms underlying such diseases are unclear, environmental and social factors, such as cigarette smoke and obesity, increase the risk of disease development. Yet, not all smokers or obese individuals will develop chronic respiratory diseases. The mitogen-activated protein kinase p38α is abnormally active in such maladies, but its contribution, if any, to disease etiology is unknown. To assess whether p38α activation per se in the lung could impose disease symptoms, we generated a transgenic mouse model allowing controllable expression of an intrinsically active variant, p38αD176A+F327S, specifically in lung alveolar type 2 pneumocytes. Sustained expression of p38αD176A+F327S did not appear to induce obvious pathological outcomes or to exacerbate inflammatory outcomes in mice challenged with common respiratory disease triggers. However, mice expressing p38αD176A+F327S in alveolar type 2 cells and fed with a high-fat diet exhibited increased numbers of airway eosinophils and lymphocytes, upregulated levels of proinflammatory cytokines and chemokines including interleukin-1β and eotaxin, as well as a reduction in levels of leptin and adiponectin within the lung. Neither high-fat diet nor p38αD176A+F327S alone induced such outcomes. Perhaps in obese individuals with associated respiratory diseases, elevated p38α activity which happens to occur is the factor that promotes their development.

Quercetin attenuates lipopolysaccharide-induced hepatic inflammation by modulating autophagy and necroptosis

Lipopolysaccharide (LPS) from Gram-negative bacteria initially induces liver inflammation with proinflammatory cytokines expressions. However, the underlying hepatoprotective mechanism of quercetin on LPS-induced hepatic inflammation remains unclear. Specific pathogen-free chicken embryos (n = 120) were allocated control vehicle, PBS with or without ethanol vehicle, LPS (125 ng/egg) with or without quercetin treatment (10, 20, or 40 nmol/egg, respectively), quercetin groups (10, 20, or 40 nmol/egg). Fifteen-day-old embryonated eggs were inoculated abovementioned solutions via the allantoic cavity. At embryonic d 19, the livers of the embryos were collected for histopathological examination, RNA extraction, real-time polymerase chain reaction, and immunohistochemistry investigation. We found that the liver presented inflammatory response (heterophils infiltration) after LPS induction. The LPS-induced mRNA expressions of inflammation-related factors (TLR4, TNFα, IL-1β, IL-10, IL-6, MYD88, NF-κB1, p38, and MMP3) were upregulated after LPS induction when compared with the PBS group, while quercetin could downregulate these expressions as compared with the LPS group. Quercetin significantly decreased the immunopositivity to TLR4 and MMP3 in the treatment group when compared with the LPS group. Quercetin could significantly downregulate the mRNA expressions of autophagy-related genes (ATG5, ATG7, Beclin-1, LC3A, and LC3B) and necroptosis-related genes (Fas, Bcl-2, Drp1, and RIPK1) after LPS induction. Quercetin significantly decreased the immunopositivity to LC3 in the treatment group when compared with the LPS group; meanwhile, quercetin significantly decreased the protein expressions of LC3-I, LC3-II, and the rate of LC3-II/LC3-I. In conclusions, quercetin can alleviate hepatic inflammation induced by LPS through modulating autophagy and necroptosis.

The role of the canonical nf-κb signaling pathway in the development of acute liver failure

As a clinical emergency with a high mortality rate, the treatment of acute liver failure has been paid attention to by society. At present, liver transplantation is the most effective treatment for acute liver failure, but there is still an insufficient supply of liver sources and a poor prognosis. In view of the current therapeutic development of this disease, more researchers have turned their attention to the research of drugs related to the NF-κB pathway. The NF-κB canonical pathway has been proven to play a role in a variety of diseases, regulating inflammation, apoptosis, and other physiological processes. More and more evidence shows that the NF-κB canonical pathway regulates the pathogenesis of acute liver failure. In this review, we will summarize the regulation process of the NF-κB canonical pathway on acute liver failure, and develop a new way to treat acute liver failure by targeting the components of the pathway.

Systematic analysis of the MAPK signaling network reveals MAP3K-driven control of cell fate

The classic network of mitogen-activated protein kinases (MAPKs) is highly interconnected and controls a diverse array of biological processes. In multicellular eukaryotes, the MAPKs ERK, JNK, and p38 control opposing cell behaviors but are often activated simultaneously, raising questions about how input-output specificity is achieved. Here, we use multiplexed MAPK activity biosensors to investigate how cell fate control emerges from the connectivity and dynamics of the MAPK network. Through chemical and genetic perturbation, we systematically explore the outputs and functions of all the MAP3 kinases encoded in the human genome and show that MAP3Ks control cell fate by triggering unique combinations of MAPK activity. We show that these MAPK activity combinations explain the paradoxical dual role of JNK signaling as pro-apoptotic or pro-proliferative kinase. Overall, our integrative analysis indicates that the MAPK network operates as a unit to control cell fate and shifts the focus from MAPKs to MAP3Ks to better understand signaling-mediated control of cell fate.

Alzheimer's disease: Ablating single master site abolishes tau hyperphosphorylation

Hyperphosphorylation of the neuronal tau protein is a hallmark of neurodegenerative tauopathies such as Alzheimer's disease. A central unanswered question is why tau becomes progressively hyperphosphorylated. Here, we show that tau phosphorylation is governed by interdependence- a mechanistic link between initial site-specific and subsequent multi-site phosphorylation. Systematic assessment of site interdependence identified distinct residues (threonine-50, threonine-69, and threonine-181) as master sites that determine propagation of phosphorylation at multiple epitopes. CRISPR point mutation and expression of human tau in Alzheimer's mice showed that site interdependence governs physiologic and amyloid-associated multi-site phosphorylation and cognitive deficits, respectively. Combined targeting of master sites and p38α, the most central tau kinase linked to interdependence, synergistically ablated hyperphosphorylation. In summary, our work delineates how complex tau phosphorylation arises to inform therapeutic and biomarker design for tauopathies.

Total C-21 Steroidal Glycosides From Baishouwu Ameliorate Hepatic and Renal Fibrosis by Regulating IL-1β/MyD88 Inflammation Signaling

Fibrosis is a worldwide public health problem, which typically results from chronic diseases and often leads to organ malfunction. Chronic inflammation has been suggested to be the major trigger for fibrogenesis, yet mechanisms by which inflammatory signals drive fibrogenesis have not been fully elucidated. Total C-21 steroidal glycosides (TCSG) from Baishouwu are the main active components of the root of Cynanchum auriculatum Royle ex Wight, which exert hepatoprotective and anti-inflammation properties. In this study, we established a mouse model with the coexistence of hepatic and renal fibrosis and aimed to investigate the effects of TCSG from Baishouwu on fibrosis and explored the potential mechanisms. The results of biochemical and pathological examinations showed that TCSG from Baishouwu improved liver and kidney function and alleviated hepatic and renal fibrosis by reducing collagen and extracellular matrix deposition in bile duct ligation and unilateral ureteral occlusion (BDL&UUO) mice. According to network pharmacology analysis, the mechanisms underlying the effects of TCSG from Baishouwu on hepatic and renal fibrosis were associated with inflammatory response pathways, including “Signaling by interleukins”, “MAP kinase activation”, “MyD88 cascade initiated on plasma membrane”, and “Interleukin-1 family signaling”. Regression analysis and western blot results revealed that IL-1β/MyD88 inflammation signaling played an essential role in the anti-fibrotic effects of TCSG from Baishouwu. Further data displayed that TCSG from Baishouwu affected inflammatory response and extracellular matrix deposition via suppressing the activation of p38 MAPK/JNK and NF-κB p65 signaling cascades both in the liver and kidney of BDL&UUO mice. Thus, our findings suggest TCSG from Baishouwu as a natural regimen against hepatic and renal fibrosis and provide direct evidence that IL-1β/MyD88 signaling crucially contributes to hepatic and renal fibrosis and modulates liver-kidney crosstalk by maintaining tight control over inflammatory responses.

JNK signaling prevents biliary cyst formation through a CASPASE-8-dependent function of RIPK1 during aging

JNK signaling has been studied intensively in models of liver physiology and disease, but previous studies had focused on young mice. However, it had not been recognized that JNK plays a fundamental role in maintaining liver homeostasis and preventing the formation of biliary cysts in aging mice. These observations call for caution in all long-term pharmacological inhibition strategies targeting the JNK pathway. Finally, our results provide evidence of a molecular link between JNK and the cell-death mediator RIPK1. The specific overexpression of RIPK1 in cysts of a subset of patients with polycystic liver disease suggests that RIPK1 might be mechanistically involved in the pathogenesis of human biliary cysts.

The c-Jun N-terminal kinase (JNK) signaling pathway mediates adaptation to stress signals and has been associated with cell death, cell proliferation, and malignant transformation in the liver. However, up to now, its function was experimentally studied mainly in young mice. By generating mice with combined conditional ablation of Jnk1 and Jnk2 in liver parenchymal cells (LPCs) (JNK1/2^LPC-KO mice; KO, knockout), we unraveled a function of the JNK pathway in the regulation of liver homeostasis during aging. Aging JNK1/2^LPC-KO mice spontaneously developed large biliary cysts that originated from the biliary cell compartment. Mechanistically, we could show that cyst formation in livers of JNK1/2^LPC-KO mice was dependent on receptor-interacting protein kinase 1 (RIPK1), a known regulator of cell survival, apoptosis, and necroptosis. In line with this, we showed that RIPK1 was overexpressed in the human cyst epithelium of a subset of patients with polycystic liver disease. Collectively, these data reveal a functional interaction between JNK signaling and RIPK1 in age-related progressive cyst development. Thus, they provide a functional linkage between stress adaptation and programmed cell death (PCD) in the maintenance of liver homeostasis during aging.

LR12 Promotes Liver Repair by Improving the Resolution of Inflammation and Liver Regeneration in Mice with Thioacetamide- (TAA-) Induced Acute Liver Failure

Background

Triggering receptor expressed on myeloid cells-1 (TREM-1) controls the mobilization of inflammatory cells in response to injury and consequently enhances liver damage. LR12 is a TREM-1 inhibitory peptide. However, the role of LR12 in acute liver failure (ALF) has remained elusive. This study was aimed at indicating whether LR12 could promote liver repair in mice with thioacetamide- (TAA-) induced ALF.

Methods

BALB/c mice were intraperitoneally injected with TAA, followed by intravenous injection of LR12. Damage and regeneration of the liver were assessed. LO2 cells and macrophages were used to assess the therapeutic effects of LR12.

Results

Mice treated with TAA for 24 h developed ALF, while liver inflammation was alleviated after LR12 treatment. Moreover, LR12 promoted hepatocyte regeneration in mice with TAA-induced ALF. In vitro, the supernatant from TAA+LR12-treated macrophages promoted the proliferation of LO2 cells. Cytokine protein microarray analysis suggested that LR12 promoted the secretion of C-C chemokine ligand 20 (CCL20) from macrophages. Besides, neutralization of CCL20 blocked the effects of LR12, thus inhibited the proliferation of LO2 cells in vitro, aggregated the liver inflammation, and restrained hepatocyte regeneration in ALF mice in vivo. Furthermore, we also found that LR12 activated the p38 mitogen-activated protein kinase (MAPK) pathway in hepatocytes through promoting the secretion of CCL20 from macrophages.

Conclusions

LR12 could improve the resolution of inflammation and liver regeneration in mice with TAA-induced ALF by promoting the secretion of CCL20 from macrophages and activating the p38 MAPK pathway. Therefore, LR12 could be an attractive therapeutic target for the treatment of ALF.

The Role of Histone Acetylation-/Methylation-Mediated Apoptotic Gene Regulation in Hepatocellular Carcinoma

Epigenetics, an inheritable phenomenon, which influences the expression of gene without altering the DNA sequence, offers a new perspective on the pathogenesis of hepatocellular carcinoma (HCC). Nonalcoholic steatohepatitis (NASH) is projected to account for a significant share of HCC incidence due to the growing prevalence of various metabolic disorders. One of the major molecular mechanisms involved in epigenetic regulation, post-translational histone modification seems to coordinate various aspects of NASH which will further progress to HCC. Mounting evidence suggests that the orchestrated events of cellular and nuclear changes during apoptosis can be regulated by histone modifications. This review focuses on the current advances in the study of acetylation-/methylation-mediated histone modification in apoptosis and the implication of these epigenetic regulations in HCC. The reversibility of epigenetic alterations and the agents that can target these alterations offers novel therapeutic approaches and strategies for drug development. Further molecular mechanistic studies are required to enhance information governing these epigenetic modulators, which will facilitate the design of more effective diagnosis and treatment options.

Functions of p38 MAP Kinases in the Central Nervous System

Mitogen-activated protein (MAP) kinases are a central component in signaling networks in a multitude of mammalian cell types. This review covers recent advances on specific functions of p38 MAP kinases in cells of the central nervous system. Unique and specific functions of the four mammalian p38 kinases are found in all major cell types in the brain. Mechanisms of p38 activation and downstream phosphorylation substrates in these different contexts are outlined and how they contribute to functions of p38 in physiological and under disease conditions. Results in different model organisms demonstrated that p38 kinases are involved in cognitive functions, including functions related to anxiety, addiction behavior, neurotoxicity, neurodegeneration, and decision making. Finally, the role of p38 kinases in psychiatric and neurological conditions and the current progress on therapeutic inhibitors targeting p38 kinases are covered and implicate p38 kinases in a multitude of CNS-related physiological and disease states.

The IL-33-induced p38-/JNK1/2-TNFα axis is antagonized by activation of β-adrenergic-receptors in dendritic cells

IL-33, an IL-1 cytokine superfamily member, induces the activation of the canonical NF-κB signaling, and of Mitogen Activated Protein Kinases (MAPKs). In dendritic cells (DCs) IL-33 induces the production of IL-6, IL-13 and TNFα. Thereby, the production of IL-6 depends on RelA whereas the production of IL-13 depends on the p38-MK2/3 signaling module. Here, we show that in addition to p65 and the p38-MK2/3 signaling module, JNK1/2 are essential for the IL-33-induced TNFα production. The central roles of JNK1/2 and p38 in DCs are underpinned by the fact that these two MAPK pathways are controlled by activated β-adrenergic receptors resulting in a selective regulation of the IL-33-induced TNFα response in DCs.

Mapping p38α mitogen-activated protein kinase signaling by proximity-dependent labeling

Mitogen-activated protein (MAP) kinase signaling is central to multiple cellular responses and processes. MAP kinase p38α is the best characterized member of the p38 MAP kinase family. Upstream factors and downstream targets of p38α have been identified in the past by conventional methods such as coimmunoprecipitation. However, a complete picture of its interaction partners and substrates in cells is lacking. Here, we employ a proximity-dependent labeling approach using biotinylation tagging to map the interactome of p38α in cultured 293T cells. Fusing the advanced biotin ligase BioID2 to the N-terminus of p38α, we used mass spectrometry to identify 37 biotin-labeled proteins that putatively interact with p38α. Gene ontology analysis confirms known upstream and downstream factors in the p38 MAP kinase cascade (e.g., MKK3, MAPKAPK2, TAB2, and c-jun). We furthermore identify a cluster of zinc finger (ZnF) domain-containing proteins that is significantly enriched among proximity-labeled interactors and is involved in gene transcription and DNA damage response. Fluorescence imaging and coimmunoprecipitation with overexpressed p38α in cells supports an interaction of p38α with ZnF protein XPA, a key factor in the DNA damage response, that is promoted by UV irradiation. These results define an extensive network of interactions of p38α in cells and new direct molecular targets of MAP kinase p38α in gene regulation and the DNA damage response.

Anxiety in rats with bile duct ligation is associated with activation of JNK3 mitogen-activated protein kinase in the hippocampus

We examine the anxiety-like behaviors in rats with bile duct ligation (BDL), as well as its relationship with the expression of JNK3 and P38 MAPKs in rat hippocampus. Male Wistar rats undergo either sham operation or BDL as a rat model of cirrhotic HE. The anxiety-like behaviors are determined using a light/dark box test two hours befor the surgery on day 1 and on days 7, 14, 21 and 28 of BDL. The gene and protein expression levels of JNK3 and p38 in the hippocampus were examined respectively with qPCR and western blotting methods on day 28 of BDL. The results revealed that anxiety was increased in the cirrhotic HE model rats during 28 days of BDL. The molecular data indicated that the gene expression of Jnk3 and protein levels of JNK3, as well as phospho-JNK3, significantly increased in the hippocampus of the cirrhotic HE model rats compared to the sham control group. However, the results revealed no significant changes in the gene expression and the protein levels of p38 as well as phospho-p38 in the hippocampus of the cirrhotic HE model rats compared to the sham control group. We conclude that the increases in the expression and activation of JNK3 MAPK in the hippocampus may underlie, at least partly, the anxiety-like behaviors in rats with cirrhotic HE.

Requirement for epithelial p38α in KRAS-driven lung tumor progression

Malignant transformation entails important changes in the control of cell proliferation through the rewiring of selected signaling pathways. Cancer cells then become very dependent on the proper function of those pathways, and their inhibition offers therapeutic opportunities. Here we identify the stress kinase p38α as a nononcogenic signaling molecule that enables the progression of Kras^G12V-driven lung cancer. We demonstrate in vivo that, despite acting as a tumor suppressor in healthy alveolar progenitor cells, p38α contributes to the proliferation and malignization of lung cancer epithelial cells. We show that high expression levels of p38α correlate with poor survival in lung adenocarcinoma patients, and that genetic or chemical inhibition of p38α halts tumor growth in lung cancer mouse models. Moreover, we reveal a lung cancer epithelial cell-autonomous function for p38α promoting the expression of TIMP-1, which in turn stimulates cell proliferation in an autocrine manner. Altogether, our results suggest that epithelial p38α promotes Kras^G12V-driven lung cancer progression via maintenance of cellular self-growth stimulatory signals.

Predisposition to Apoptosis in Hepatocellular Carcinoma: From Mechanistic Insights to Therapeutic Strategies

Hepatocellular carcinoma (HCC) ranks among the most rapidly evolving cancers in the Western world. The majority of HCCs develop on the basis of a chronic inflammatory liver damage that predisposes liver cancer development and leads to deregulation of multiple cellular signaling pathways. The resulting dysbalance between uncontrolled proliferation and impaired predisposition to cell death with consecutive failure to clear inflammatory damage is a key driver of malignant transformation. Therefore, resistance to death signaling accompanied by metabolic changes as well as failed immunological clearance of damaged pre-neoplastic hepatocytes are considered hallmarks of hepatocarcinogenesis. Hereby, the underlying liver disease, the type of liver damage and individual predisposition to apoptosis determines the natural course of the disease as well as the therapeutic response. Here, we will review common and individual aspects of cell death pathways in hepatocarcinogenesis with a particular emphasis on regulatory networks and key molecular alterations. We will further delineate the potential of targeting cell death-related signaling as a viable therapeutic strategy to improve the outcome of HCC patients.

Cell-to-Cell Heterogeneity in p38-Mediated Cross-Inhibition of JNK Causes Stochastic Cell Death

The stress-activated protein kinases c-Jun N-terminal kinase (JNK) and p38 are important players in cell-fate decisions in response to environmental stress signals. Crosstalk signaling between JNK and p38 is emerging as an important regulatory mechanism in inflammatory and stress responses. However, it is unknown how this crosstalk affects signaling dynamics, cell-to-cell variation, and cellular responses at the single-cell level. We established a multiplexed live-cell imaging system based on kinase translocation reporters to simultaneously monitor JNK and p38 activities with high specificity and sensitivity at single-cell resolution. Various stresses activated JNK and p38 with various dynamics. In all cases, p38 suppressed JNK activity in a cross-inhibitory manner. We demonstrate that p38 antagonizes JNK through both transcriptional and post-translational mechanisms. This cross-inhibition generates cellular heterogeneity in JNK activity after stress exposure. Our data indicate that this heterogeneity in JNK activity plays a role in fractional killing in response to UV stress.

Hepatospecific ablation of p38α MAPK governs liver regeneration through modulation of inflammatory response to CCl4-induced acute injury

Mammalian p38α MAPK (Mitogen-Activated Protein Kinase) transduces a variety of extracellular signals that regulate cellular processes, such as inflammation, differentiation, proliferation or apoptosis. In the liver, depending of the physiopathological context, p38α acts as a negative regulator of hepatocyte proliferation as well as a promotor of inflammatory processes. However, its function during an acute injury, in adult liver, remains uncharacterized. In this study, using mice that are deficient in p38α specifically in mature hepatocytes, we unexpectedly found that lack of p38α protected against acute injury induced by CCl₄ compound. We demonstrated that the hepatoprotective effect alleviated ROS accumulation and shaped the inflammatory response to promote efficient tissue repair. Mechanistically, we provided strong evidence that Ccl2/Ccl5 chemokines were crucial for a proper hepatoprotective response observed secondary to p38α ablation. Indeed, antibody blockade of Ccl2/Ccl5 was sufficient to abrogate hepatoprotection through a concomitant decrease of both inflammatory cells recruitment and antioxidative response that result ultimately in higher liver damages. Our findings suggest that targeting p38α expression and consequently orientating immune response may represent an attractive approach to favor tissue recovery after acute liver injury.

Context-Dependent Role of NF-κB Signaling in Primary Liver Cancer-from Tumor Development to Therapeutic Implications

Chronic inflammatory cell death is a major risk factor for the development of diverse cancers including liver cancer. Herein, disruption of the hepatic microenvironment as well as the immune cell composition are major determinants of malignant transformation and progression in hepatocellular carcinomas (HCC). Considerable research efforts have focused on the identification of predisposing factors that promote induction of an oncogenic field effect within the inflammatory liver microenvironment. Among the most prominent factors involved in this so-called inflammation-fibrosis-cancer axis is the NF-κB pathway. The dominant role of this pathway for malignant transformation and progression in HCC is well documented. Pathway activation is significantly linked to poor prognostic traits as well as stemness characteristics, which places modulation of NF-κB signaling in the focus of therapeutic interventions. However, it is well recognized that the mechanistic importance of the pathway for HCC is highly context and cell type dependent. While constitutive pathway activation in an inflammatory etiological background can significantly promote HCC development and progression, absence of NF-κB signaling in differentiated liver cells also significantly enhances liver cancer development. Thus, therapeutic targeting of NF-κB as well as associated family members may not only exert beneficial effects but also negatively impact viability of healthy hepatocytes and/or cholangiocytes, respectively. The review presented here aims to decipher the complexity and paradoxical functions of NF-κB signaling in primary liver and non-parenchymal cells, as well as the induced molecular alterations that drive HCC development and progression with a particular focus on (immune-) therapeutic interventions.

Regulation of tumor angiogenesis and mesenchymal-endothelial transition by p38α through TGF-β and JNK signaling

The formation of new blood vessels is essential for normal development, tissue repair and tumor growth. Here we show that inhibition of the kinase p38α enhances angiogenesis in human and mouse colon tumors. Mesenchymal cells can contribute to tumor angiogenesis by regulating proliferation and migration of endothelial cells. We show that p38α negatively regulates an angiogenic program in mesenchymal stem/stromal cells (MSCs), multipotent progenitors found in perivascular locations. This program includes the acquisition of an endothelial phenotype by MSCs mediated by both TGF-β and JNK, and negatively regulated by p38α. Abrogation of p38α in mesenchymal cells increases tumorigenesis, which correlates with enhanced angiogenesis. Using genetic models, we show that p38α regulates the acquisition of an endothelial-like phenotype by mesenchymal cells in colon tumors and damage tissue. Taken together, our results indicate that p38α in mesenchymal cells restrains a TGF-β-induced angiogenesis program including their ability to transdifferentiate into endothelial cells.

Mesenchymal cells contribute to tumor angiogenesis by regulating proliferation and migration of endothelial cells. Here, the authors show that mesenchymal stem cells also have the ability to acquire an endothelial phenotype upon TGF-β stimulation via the downstream kinase JNK, and that p38α negatively regulates this process.

Pro-apoptotic and anti-angiogenic actions of 2-methoxyestradiol and docosahexaenoic acid, the biologically derived active compounds from flaxseed diet, in preventing ovarian cancer

BACKGROUND

We have previously shown that a whole flaxseed supplemented diet decreased the onset and severity of ovarian cancer in the laying hen, the only known animal model of spontaneous ovarian cancer. Flaxseed is rich in omega-3 fatty acids (OM3FA), mostly α-Linoleic acid (ALA), which gets converted to Docosahexaenoic acid (DHA) by the action of delta-6 desaturase enzyme. Ingestion of flaxseed also causes an increase in production of 2-methoxyestradiol (2MeOE2) via the induction of the CYP1A1 pathway of estrogen metabolism. We have previously reported that the flaxseed diet induces apoptosis via p38-MAPK pathway in chicken tumors. The objective of this study was to investigate the effect of the flaxseed diet on ovarian cancer in chickens, focusing on two hallmarks of cancer, apoptosis and angiogenesis.

RESULTS

The anti-cancer effects of two active biologically derived compounds of flax diet, 2MeOE2 and DHA, were individually tested on human ovarian cancer cells and in vivo by the Chick Chorioallantoic Membrane (CAM) assay. Our results indicate that a flaxseed-supplemented diet promotes apoptosis and inhibits angiogenesis in chicken tumors but not in normal ovaries. 2MeOE2 promotes apoptosis in human ovarian cancer cells, inhibits angiogenesis on CAM and its actions are dependent on the p38-MAPK pathway. DHA does not have any pro-apoptotic effect on human ovarian cancer cells but has strong anti-angiogenic effects as seen on CAM, but not dependent on the p38-MAPK pathway.

CONCLUSIONS

Dietary flaxseed supplementation promotes a pro-apoptotic and anti-angiogenic effect in ovarian tumors, not in normal ovaries. The biologically derived active compounds from flaxseed diet act through different pathways to elicit their respective anti-cancer effects. A flaxseed-supplemented diet is a promising approach for prevention of ovarian cancer as well as having a significant potential as an adjuvant treatment to supplement chemotherapeutic agents for treatment of advanced stages of ovarian cancer.

The Regulation of JNK Signaling Pathways in Cell Death through the Interplay with Mitochondrial SAB and Upstream Post-Translational Effects

c-Jun-N-terminal kinase (JNK) activity plays a critical role in modulating cell death, which depends on the level and duration of JNK activation. The kinase cascade from MAPkinase kinase kinase (MAP3K) to MAPkinase kinase (MAP2K) to MAPKinase (MAPK) can be regulated by a number of direct and indirect post-transcriptional modifications, including acetylation, ubiquitination, phosphorylation, and their reversals. Recently, a JNK-mitochondrial SH3-domain binding protein 5 (SH3BP5/SAB)-ROS activation loop has been elucidated, which is required to sustain JNK activity. Importantly, the level of SAB expression in the outer membrane of mitochondria is a major determinant of the set-point for sustained JNK activation. SAB is a docking protein and substrate for JNK, leading to an intramitochondrial signal transduction pathway, which impairs electron transport and promotes reactive oxygen species (ROS) release to sustain the MAPK cascade.

Neuronal MAP kinase p38α inhibits c-Jun N-terminal kinase to modulate anxiety-related behaviour

Modulation of behavioural responses by neuronal signalling pathways remains incompletely understood. Signalling via mitogen-activated protein (MAP) kinase cascades regulates multiple neuronal functions. Here, we show that neuronal p38α, a MAP kinase of the p38 kinase family, has a critical and specific role in modulating anxiety-related behaviour in mice. Neuron-specific p38α-knockout mice show increased levels of anxiety in behaviour tests, yet no other behavioural, cognitive or motor deficits. Using CRISPR-mediated deletion of p38α in cells, we show that p38α inhibits c-Jun N-terminal kinase (JNK) activity, a function that is specific to p38α over other p38 kinases. Consistently, brains of neuron-specific p38α-knockout mice show increased JNK activity. Inhibiting JNK using a specific blood-brain barrier-permeable inhibitor reduces JNK activity in brains of p38α-knockout mice to physiological levels and reverts anxiety behaviour. Thus, our results suggest that neuronal p38α negatively regulates JNK activity that is required for specific modulation of anxiety-related behaviour.

Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism

Recent studies suggest that cardiac fibroblast-specific p38α MAPK contributes to the development of cardiac hypertrophy, but the underlying mechanism is unknown. Our study used a novel fibroblast-specific, tamoxifen-inducible p38α knockout (KO) mouse line to characterize the role of fibroblast p38α in modulating cardiac hypertrophy, and we elucidated the mechanism. Myocardial injury was induced in tamoxifen-treated Cre-positive p38α KO mice or control littermates via chronic infusion of the β-adrenergic receptor agonist isoproterenol. Cardiac function was assessed by pressure-volume conductance catheter analysis and was evaluated for cardiac hypertrophy at tissue, cellular, and molecular levels. Isoproterenol infusion in control mice promoted overt cardiac hypertrophy and dysfunction (reduced ejection fraction, increased end systolic volume, increased cardiac weight index, increased cardiomyocyte area, increased fibrosis, and up-regulation of myocyte fetal genes and hypertrophy-associated microRNAs). Fibroblast-specific p38α KO mice exhibited marked protection against myocardial injury, with isoproterenol-induced alterations in cardiac function, histology, and molecular markers all being attenuated. In vitro mechanistic studies determined that cardiac fibroblasts responded to damaged myocardium by secreting several paracrine factors known to induce cardiomyocyte hypertrophy, including IL-6, whose secretion was dependent upon p38α activity. In conclusion, cardiac fibroblast p38α contributes to cardiomyocyte hypertrophy and cardiac dysfunction, potentially via a mechanism involving paracrine fibroblast-to-myocyte IL-6 signaling.-Bageghni, S. A., Hemmings, K. E., Zava, N., Denton, C. P., Porter, K. E., Ainscough, J. F. X., Drinkhill, M. J., Turner, N. A. Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism.

Age-dependent regulation of antioxidant genes by p38α MAPK in the liver

p38α is a redox sensitive MAPK activated by pro-inflammatory cytokines and environmental, genotoxic and endoplasmic reticulum stresses. The aim of this work was to assess whether p38α controls the antioxidant defense in the liver, and if so, to elucidate the mechanism(s) involved and the age-related changes. For this purpose, we used liver-specific p38α-deficient mice at two different ages: young-mice (4 months-old) and old-mice (24 months-old). The liver of young p38α knock-out mice exhibited a decrease in GSH levels and an increase in GSSG/GSH ratio and malondialdehyde levels. However, old mice deficient in p38α had higher hepatic GSH levels and lower GSSG/GSH ratio than young p38α knock-out mice. Liver-specific p38α deficiency triggered a dramatic down-regulation of the mRNAs of the key antioxidant enzymes glutamate cysteine ligase, superoxide dismutase 1, superoxide dismutase 2, and catalase in young mice, which seems mediated by the lack of p65 recruitment to their promoters. Nrf-2 nuclear levels did not change significantly in the liver of young mice upon p38α deficiency, but nuclear levels of phospho-p65 and PGC-1α decreased in these mice. p38α-dependent activation of NF-κB seems to occur through classical IκB Kinase and via ribosomal S6 kinase1 and AKT in young mice. However, unexpectedly the long-term deficiency in p38α triggers a compensatory up-regulation of antioxidant enzymes via NF-κB activation and recruitment of p65 to their promoters. In conclusion, p38α MAPK maintains the expression of antioxidant genes in liver of young animals via NF-κΒ under basal conditions, whereas its long-term deficiency triggers compensatory up-regulation of antioxidant enzymes through NF-κΒ.

Loss of cellular FLICE-inhibitory protein promotes acute cholestatic liver injury and inflammation from bile duct ligation

Cholestatic liver injury results from impaired bile flow or metabolism and promotes hepatic inflammation and fibrogenesis. Toxic bile acids that accumulate in cholestasis induce apoptosis and contribute to early cholestatic liver injury, which is amplified by accompanying inflammation. The aim of the current study was to evaluate the role of the antiapoptotic caspase 8-homolog cellular FLICE-inhibitory (cFLIP) protein during acute cholestatic liver injury. Transgenic mice exhibiting hepatocyte-specific deletion of cFLIP (cFLIP^-/-) were used for in vivo and in vitro analysis of cholestatic liver injury using bile duct ligation (BDL) and the addition of bile acids ex vivo. Loss of cFLIP in hepatocytes promoted acute cholestatic liver injury early after BDL, which was characterized by a rapid release of proinflammatory and chemotactic cytokines (TNF, IL-6, IL-1β, CCL2, CXCL1, and CXCL2), an increased presence of CD68⁺ macrophages and an influx of neutrophils in the liver, and resulting apoptotic and necrotic hepatocyte cell death. Mechanistically, liver injury in cFLIP^-/- mice was aggravated by reactive oxygen species, and sustained activation of the JNK signaling pathway. In parallel, cytoprotective NF-κB p65, A20, and the MAPK p38 were inhibited. Increased injury in cFLIP^-/- mice was accompanied by activation of hepatic stellate cells and profibrogenic regulators. The antagonistic caspase 8-homolog cFLIP is a critical regulator of acute, cholestatic liver injury. NEW & NOTEWORTHY The current paper explores the role of a classical modulator of hepatocellular apoptosis in early, cholestatic liver injury. These include activation of NF-κB and MAPK signaling, production of inflammatory cytokines, and recruitment of neutrophils in response to cholestasis. Because these signaling pathways are currently exploited in clinical trials for the treatment of nonalcoholic steatohepatitis and cirrhosis, the current data will help in the development of novel pharmacological options in these indications.

Regulation of Mammary Luminal Cell Fate and Tumorigenesis by p38α

Mammary stem and progenitor cells are essential for mammary gland homeostasis and are also candidates for cells of origin of mammary tumors. Here, we have investigated the function of the protein kinase p38α in the mammary gland using mice that delete this protein in the luminal epithelial cells. We show that p38α regulates the fate of luminal progenitor cells through modulation of the transcription factor RUNX1, an important controller of the estrogen receptor-positive cell lineage. We also provide evidence that the regulation of RUNX1 by p38α probably involves the kinase MSK1, which phosphorylates histone H3 at the RUNX1 promoter. Moreover, using a mouse model for breast cancer initiated by luminal cells, we show that p38α downregulation in mammary epithelial cells reduces tumor burden, which correlates with decreased numbers of tumor-initiating cells. Collectively, our results define a key role for p38α in luminal progenitor cell fate that affects mammary tumor formation.

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Luminal progenitor cell fate in the mammary gland is regulated by p38α

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p38α controls the ER transcriptional program by modulating RUNX1

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p38α regulates H3 phosphorylation at the RUNX1 promoter through the kinase MSK1

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p38α promotes mammary tumorigenesis by maintaining luminal tumor-initiating cells

p38α MAPK antagonizing JNK to control the hepatic fat accumulation in pediatric patients onset intestinal failure

The p38α mitogen-activated protein kinase (MAPK) has been related to gluconeogenesis and lipid metabolism. However, the roles and related mechanisms of p38α MAPK in intestinal failure (IF)-associated liver steatosis remained poor understood. Here, our experimental evidence suggested that p38α MAPK significantly suppressed the fat accumulation in livers of IF patients mainly through two mechanisms. On the one hand, p38α MAPK increased hepatic bile acid (BA) synthesis by upregulating the expression of the rate-limiting enzyme cholesterol 7-α-hydroxylase (CYP7A1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which in turn activated the transcription of the CYP7A1. On the other hand, p38α MAPK promoted fatty acid (FA) β-oxidation via upregulating peroxisome proliferator-activated receptor alpha (PPARα) and its transcriptional target genes carnitine palmitoyltransferase 1A (CPT1A) and peroxisomal acyl-coenzyme aoxidase 1 (ACOX1). Dual luciferase assays indicated that p38α MAPK increased the transcription of PPARα, PGC-1α and CYP7A1 by upregulating their promoters’ activities. In addition, in vitro and in vivo assays indicated p38α MAPK negatively regulates the hepatic steatosis by controlling JNK activation. In conculsion, our findings demonstrate that hepatic p38α MAPK functions as a negative regulator of liver steatosis in maintaining BA synthesis and FAO by antagonizing the c-Jun N-terminal kinase (JNK).

Inactivation of JNK2 as carcinogenic factor in colitis-associated and sporadic colorectal carcinogenesis

We recently reported that dysregulated c-Jun N-terminal kinases (JNK) activity causes defective cell cycle checkpoint control, inducing neoplastic transformation in a cellular ulcerative colitis (UC) model. In the quiescent chronic phase of UC, p-p54 JNK was down-regulated and p-p46 JNK was up-regulated. Both were up-regulated in the acute phase. Consequently, increased p21WAF1 and γ-H2AX, two JNK-regulated proteins, induced cell cycle arrest. Their down-regulation led to checkpoint override, causing increased proliferation and undetected DNA damage in quiescent chronic phase, all characteristics of tumorigenesis. We investigated expression of p-JNK2, p-JNK1-3, p21WAF1, γ-H2AX and Ki67 by immunohistochemistry in cases of quiescent UC (QUC), active UC (AUC), UC-dysplasia and UC-related colorectal carcinoma (UC-CRC). Comparison was made to normal healthy colorectal mucosa, sporadic adenoma and colorectal carcinoma (CRC), diverticulitis and Crohns disease (CD). We found p-JNK2 up-regulation in AUC and its early down-regulation in UC-CRC and CRC carcinogenesis. With down-regulated p-JNK2, p21WAF1 was also decreased. Ki67 was inversely expressed, showing increased proliferation early in UC-CRC and CRC carcinogenesis. p-JNK1-3 was increased in AUC and QUC. Less increased γ-H2AX in UC-CRC compared to CRC gave evidence that colitis-triggered inflammation masks DNA damage, thus contributing to neoplastic transformation. We hypothesize that JNK-dependent cell cycle arrest is important in AUC, while chronic inflammation causes dysregulated JNK activity in quiescent phase that may contribute to checkpoint override, promoting UC carcinogenesis. We suggest restoring p-JNK2 expression as a novel therapeutic strategy to early prevent the development of UC-related cancer.

Protecting the heart through MK2 modulation, toward a role in diabetic cardiomyopathy and lipid metabolism

Various signaling pathways have been identified in the heart as important players during development, physiological adaptation or pathological processes. This includes the MAPK families, particularly p38MAPK, which is involved in several key cellular processes, including differentiation, proliferation, apoptosis, inflammation, metabolism and survival. Disrupted p38MAPK signaling has been associated with several diseases, including cardiovascular diseases (CVD) as well as diabetes and its related complications. Despite efforts to translate this knowledge into therapeutic avenues, p38 inhibitors have failed in clinical trials due to adverse effects. Inhibition of MK2, a downstream target of p38, appears to be a promising alternative strategy. Targeting MK2 activity may avoid the adverse effects linked to p38 inhibition, while maintaining its beneficial effects. MK2 was first considered as a therapeutic target in inflammatory diseases such as rheumatoid polyarthritis. A growing body of evidence now supports a key role of MK2 signaling in the pathogenesis of CVD, particularly ischemia/reperfusion injury, hypertrophy, and hypertension and that its inhibition or inactivation is associated with improved heart and vascular functions. More recently, MK2 was shown to be a potential player in diabetes and related complications, particularly in liver and heart, and perturbations in calcium handling and lipid metabolism. In this review, we will discuss recent advances in our knowledge of the role of MK2 in p38MAPK-mediated signaling and the benefits of its loss of function in CVD and diabetes, with an emphasis on the roles of MK2 in calcium handling and lipid metabolism. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

The role of MAP2 kinases and p38 kinase in acute murine liver injury models

c-Jun N-terminal kinase (JNK) mediates hepatotoxicity through interaction of its phospho-activated form with a mitochondrial outer membrane protein, Sh3bp5 or Sab, leading to dephosphorylation of intermembrane Src and consequent impaired mitochondrial respiration and enhanced ROS release. ROS production from mitochondria activates MAP3 kinases, such as MLK3 and ASK1, which continue to activate a pathway to sustain JNK activation, and amplifies the toxic effect of acetaminophen (APAP) and TNF/galactosamine (TNF/GalN). Downstream of MAP3K, in various contexts MKK4 activates both JNK and p38 kinases and MKK7 activates only JNK. The relative role of MKK4 versus 7 in liver injury is largely unexplored, as is the potential role of p38 kinase, which might be a key mediator of toxicity in addition to JNK. Antisense oligonucleotides (ASO) to MKK4, MKK7 and p38 (versus scrambled control) were used for in vivo knockdown, and in some experiments PMH were used after in vivo knockdown. Mice were treated with APAP or TNF/GalN and injury assessed. MKK4 and MKK7 were expressed in liver and each was efficiently knocked down with two different ASOs. Massive liver injury and ALT elevation were abrogated by MKK4 but not MKK7 ASO pretreatment in both injury models. The protection was confirmed in PMH. Knockdown of MKK4 completely inhibited basal P-p38 in both cytoplasm and mitochondria. However, ALT levels and histologic injury in APAP-treated mice were not altered with p38 knockdown versus scrambled control. p38 knockdown significantly increased P-JNK levels in cytoplasm but not mitochondria after APAP treatment. In conclusion, MKK4 is the major MAP2K, which activates JNK in acute liver injury. p38, the other downstream target of MKK4, does not contribute to liver injury from APAP or TNF/galactosamine.

Neuronal p38α mediates synaptic and cognitive dysfunction in an Alzheimer's mouse model by controlling β-amyloid production

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by a severe and progressive neuronal loss leading to cognitive dysfunctions. Previous reports, based on the use of chemical inhibitors, have connected the stress kinase p38α to neuroinflammation, neuronal death and synaptic dysfunction. To explore the specific role of neuronal p38α signalling in the appearance of pathological symptoms, we have generated mice that combine expression of the 5XFAD transgenes to induce AD symptoms with the downregulation of p38α only in neurons (5XFAD/p38α∆-N). We found that the neuronal-specific deletion of p38α improves the memory loss and long-term potentiation impairment induced by 5XFAD transgenes. Furthermore, 5XFAD/p38α∆-N mice display reduced amyloid-β accumulation, improved neurogenesis, and important changes in brain cytokine expression compared with 5XFAD mice. Our results implicate neuronal p38α signalling in the synaptic plasticity dysfunction and memory impairment observed in 5XFAD mice, by regulating both amyloid-β deposition in the brain and the relay of this accumulation to mount an inflammatory response, which leads to the cognitive deficits.

The role of p38alpha in Schwann cells in regulating peripheral nerve myelination and repair

Myelination in the peripheral nervous system (PNS) is controlled by both positive and negative regulators within Schwann cells to ensure timely onset and correct myelin thickness for saltatory conduction by neurons. Transcription factors such as Sox10, octamer-binding transcription factor 6 (Oct6) and Krox20 form a positive regulatory network, whereas negative regulators such as cJun and Sox2 oppose myelination in Schwann cells. The role of the p38 MAPK pathway has been studied in PNS myelination, but its precise function remains unclear, with both positive and negative effects of p38 activity reported upon both myelination and processes of nerve repair. To clarify the role of p38 MAPK in the PNS, we have analysed mice with a Schwann cell-specific ablation of the major p38 isoform, p38alpha. In line with previous findings of an inhibitory role for p38 MAPK, we observe acceleration of post-natal myelination in p38alpha null nerves, a delay in myelin down-regulation following injury, together with a small increase in levels of re-myelination following injury. Finally we explored roles for p38alpha in controlling axonal regeneration and functional repair following PNS injury and observe that loss of p38alpha function in Schwann cells does not appear to affect these processes as previously reported. These studies therefore provide further proof for a role of p38 MAPK signalling in the control of myelination by Schwann cells in the PNS, but do not show an apparent role for signalling by this MAP kinase in Schwann cells controlling other elements of Wallerian degeneration and functional repair following injury. Cover Image for this issue: doi: 10.1111/jnc.13793.

Suppression of p38α MAPK Signaling in Osteoblast Lineage Cells Impairs Bone Anabolic Action of Parathyroid Hormone

Intermittent parathyroid hormone administration (iPTH) increases bone mass and strength by stimulating osteoblast number and activity. PTH exerts its anabolic effects through cAMP/protein kinase A (PKA) signaling pathway in mature osteoblasts and osteocytes. Here, we show that inactivation of the p38α MAPK-encoding gene with the use of an osteocalcin-cre transgene prevents iPTH bone anabolic action. Indeed, iPTH fails to increase insulin-like growth factor 1 expression, osteoblast number and activity, and bone formation in mice lacking p38α in osteoblasts and osteocytes. Moreover, iPTH-induced expression of receptor activator of NF-κB ligand (RANKL) and subsequent increased bone resorption are suppressed in those mice. Finally, we found that PTH activates p38α MAPK downstream of cAMP/PKA signaling pathway in mature osteoblasts. Our findings identify p38α MAPK as a key component of PTH signaling in osteoblast lineage cells and highlight its requirement in iPTH osteoanabolic activity. © 2015 American Society for Bone and Mineral Research.

Rasfonin promotes autophagy and apoptosis via upregulation of reactive oxygen species (ROS)/JNK pathway

Rasfonin is a fungal secondary metabolite demonstrating with antitumour effects. Reactive oxygen species (ROS) are formed as a natural by-product of the normal metabolism of oxygen and have important roles in cell signalling and homeostasis. Studies reported that many fungal secondary metabolites activated either autophagy or apoptosis through ROS generation. In former study, we revealed that rasfonin induced both autophagy and apoptosis, however, whether it promoted aforementioned processes via upregulation of ROS generation remains explored. In the current work, we demonstrated that rasfonin induced autophagy and apoptosis concomitant with a dramatically ROS production. N-Acetylcysteine (NAC), an often used ROS inhibitor, decreased both autophagic flux and caspase-dependent apoptosis by rasfonin. Flow cytometry analysis revealed NAC was able to reduce rasfonin-dependent apoptosis and necrosis. In methanethiosulfonate (MTS) assay, we observed that NAC significantly blocked rasfonin-induced cell viability loss. In addition, we found that rasfonin increased the phosphorylation of c-Jun NH2-terminal kinase (JNK), which was inhibited by NAC. SP600125, an inhibitor of JNK, reduced rasfonin-dependent autophagic flux and apoptosis. Moreover, we demonstrated that rasfonin inhibited the phosphorylation of both 4E-binding protein 1 (4E-BP1) and S6 kinase 1 (S6K1), two main substrates of mammalian target of rapamycin (mTOR). Collectively, rasfonin activated autophagy and apoptosis through upregulation of ROS/JNK signalling.

Ablation of p38α MAPK Signaling in Osteoblast Lineage Cells Protects Mice From Bone Loss Induced by Estrogen Deficiency

Estrogen deficiency causes bone loss by increasing the number of bone-resorbing osteoclasts. Selective p38α MAPK inhibitors prevent bone-wasting effects of estrogen withdrawal but implicated mechanisms remain to be identified. Here, we show that inactivation of the p38α-encoding gene in osteoblast lineage cells with the use of an osteocalcin-cre transgene protects mice from ovariectomy-induced bone loss (a murine model of postmenopausal osteoporosis). Ovariectomy fails to induce bone loss, increase bone resorption, and stimulate receptor activator of nuclear factor κB ligand and IL-6 expression in mice lacking p38α in osteoblasts and osteocytes. Finally, TNFα or IL-1, which are osteoclastogenic cytokines overproduced in the bone marrow under estrogen deficiency, can activate p38α signaling in osteoblasts, but those cytokines cannot enhance Rankl and Il6 expressions or increase osteoclast formation in p38a-deficient osteoblast cultures. These findings demonstrate that p38α MAPK signaling in osteoblast lineage cells mediates ovariectomy-induced bone loss by up-regulating receptor activator of nuclear factor κB ligand and IL-6 production.

A requirement of serotonergic p38α mitogen-activated protein kinase for peripheral immune system activation of CNS serotonin uptake and serotonin-linked behaviors

Alterations in central serotonin (5-hydroxytryptamine, 5-HT) neurotransmission and peripheral immune activation have been linked to multiple neuropsychiatric disorders, including depression, schizophrenia and autism. The antidepressant-sensitive 5-HT transporter (SERT, SLC6A4), a critical determinant of synaptic 5-HT inactivation, can be regulated by pro-inflammatory cytokine signaling. Systemic innate immune system activation via intraperitoneal lipopolysaccharide (LPS) injection rapidly elevates brain SERT activity and 5-HT clearance. Moreover, the pro-inflammatory cytokine interleukin (IL)-1β rapidly stimulates SERT activity in raphe nerve terminal preparations ex vivo, effects that are attenuated by pharmacological p38 MAPK inhibition. To establish a role of serotonergic p38α MAPK signaling in LPS/IL-1β-induced SERT regulation and attendant behavioral responses, we pursued studies in mice that afford conditional elimination of p38α MAPK in 5-HT neurons (p38α(5HT-)). We found p38α(5HT-) and control (p38α(5HT+)) littermates to be indistinguishable in viability and growth and to express equivalent levels of SERT protein and synaptosomal 5-HT transport activity. Consistent with pharmacological studies, however, IL-1β fails to increase SERT activity in midbrain synaptosomes prepared from p38α(5HT-) animals. Moreover, although LPS elevated plasma corticosterone and central/peripheral pro-inflammatory cytokines in p38α(5HT-) animals, elevations in midbrain SERT activity were absent nor were changes in depressive and anxiety-like behaviors observed. Our studies support an obligate role of p38α MAPK signaling in 5-HT neurons for the translation of immune activation to SERT regulation and 5-HT-modulated behaviors.

Treatment of Obese Insulin-Resistant Mice With an Allosteric MAPKAPK2/3 Inhibitor Lowers Blood Glucose and Improves Insulin Sensitivity

The prevalence of obesity-induced type 2 diabetes (T2D) is increasing worldwide, and new treatment strategies are needed. We recently discovered that obesity activates a previously unknown pathway that promotes both excessive hepatic glucose production (HGP) and defective insulin signaling in hepatocytes, leading to exacerbation of hyperglycemia and insulin resistance in obesity. At the hub of this new pathway is a kinase cascade involving calcium/calmodulin-dependent protein kinase II (CaMKII), p38α mitogen-activated protein kinase (MAPK), and MAPKAPK2/3 (MK2/3). Genetic-based inhibition of these kinases improves metabolism in obese mice. Here, we report that treatment of obese insulin-resistant mice with an allosteric MK2/3 inhibitor, compound (cmpd) 28, ameliorates glucose homeostasis by suppressing excessive HGP and enhancing insulin signaling. The metabolic improvement seen with cmpd 28 is additive with the leading T2D drug, metformin, but it is not additive with dominant-negative MK2, suggesting an on-target mechanism of action. Allosteric MK2/3 inhibitors represent a potentially new approach to T2D that is highly mechanism based, has links to human T2D, and is predicted to avoid certain adverse effects seen with current T2D drugs.

Tissue-Specific Regulation of p38α-Mediated Inflammation in Con A-Induced Acute Liver Damage

Because p38α plays a critical role in inflammation, it has been an attractive target for the development of anti-inflammation therapeutics. However, p38α inhibitors showed side effects, including severe liver toxicity, that often prevailed over the benefits in clinical studies, and the mechanism of toxicity is not clear. In this study, we demonstrate that p38α regulates the inflammatory responses in acute liver inflammation in a tissue-specific manner, and liver toxicity by p38α inhibitors may be a result of the inhibition of protective activity of p38α in the liver. Genetic ablation of p38α in T and NKT cells protected mice from liver injury in Con A-induced liver inflammation, whereas liver-specific deletion of p38α aggravated liver pathology. We found that p38α deficiency in the liver increased the expression of chemokines to recruit more inflammatory cells, indicating that p38α in the liver plays a protective anti-inflammatory role during acute liver inflammation. Therefore, our results suggest that p38α regulates the inflammatory responses in a tissue-specific manner, and that the tissue-specific p38α targeting strategies can be used for the development of an effective anti-inflammation treatment with an improved side-effect profile.

Tristetraprolin and its role in regulation of airway inflammation

Chronic inflammatory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are clinically and socioeconomically important diseases globally. Currently the mainstay of anti-inflammatory therapy in respiratory diseases is corticosteroids. Although corticosteroids have proven clinical efficacy in asthma, many asthmatic inflammatory conditions (e.g., infection, exacerbation, and severe asthma) are not responsive to corticosteroids. Moreover, despite an understanding that COPD progression is driven by inflammation, we currently do not have effective anti-inflammatory strategies to combat this disease. Hence, alternative anti-inflammatory strategies are required. p38 mitogen-activated protein kinase (MAPK) has emerged as an important signaling molecule driving airway inflammation, and pharmacological inhibitors against p38 MAPK may provide potential therapies for chronic respiratory disease. In this review, we discuss some of the recent in vitro and in vivo studies targeting p38 MAPK, but suggest that p38 MAPK inhibitors may prove less effective than originally considered because they may block anti-inflammatory molecules along with proinflammatory responses. We propose that an alternative strategy may be to target an anti-inflammatory molecule farther downstream of p38 MAPK, i.e., tristetraprolin (TTP). TTP is an mRNA-destabilizing, RNA-binding protein that enhances the decay of mRNAs, including those encoding proteins implicated in chronic respiratory diseases. We suggest that understanding the molecular mechanism of TTP expression and its temporal regulation will guide future development of novel anti-inflammatory pharmacotherapeutic approaches to combat respiratory disease.

Roles of p38α mitogen-activated protein kinase in mouse models of inflammatory diseases and cancer

The p38α mitogen‐activated protein kinase pathway not only regulates the production of inflammatory mediators, but also controls processes related to tissue homeostasis, such as cell proliferation, differentiation and survival, which are often disrupted during malignant transformation. The versatility of this signaling pathway allows for the regulation of many specific functions depending on the cell type and context. Here, we discuss mouse models that have been used to identify in vivo functions of p38α signaling in the pathogenesis of inflammatory diseases and cancer. Experiments using genetically modified mice and pharmacological inhibitors support that targeting the p38α pathway could be therapeutically useful for some inflammatory diseases and tumor types.

EGFR has a tumour-promoting role in liver macrophages during hepatocellular carcinoma formation

Hepatocellular carcinoma (HCC) is a frequent cancer with limited treatment options and poor prognosis. Tumorigenesis has been linked with macrophage-mediated chronic inflammation and diverse signaling pathways including the Epidermal Growth Factor Receptor (EGFR) pathway. The precise role of EGFR in HCC is unknown, and EGFR-inhibitors have shown disappointing clinical results. Here we discover that EGFR is expressed in liver macrophages in both human HCC and in a mouse HCC model. Mice lacking EGFR in macrophages show impaired hepatocarcinogenesis, whereas mice lacking EGFR in hepatocytes unexpectedly develop more HCC due to increased hepatocyte damage and compensatory proliferation. Mechanistically, following IL-1 stimulation, EGFR is required in liver macrophages to transcriptionally induce IL-6, which triggers hepatocyte proliferation and HCC. Importantly, the presence of EGFR-positive liver macrophages in HCC-patients is associated with poor survival. This study demonstrates a tumor-promoting mechanism for EGFR in non-tumor cells, which could lead to more effective precision medicine strategies.

The p38α MAPK function in osteoprecursors is required for bone formation and bone homeostasis in adult mice

BACKGROUND

p38 MAPK activity plays an important role in several steps of the osteoblast lineage progression through activation of osteoblast-specific transcription factors and it is also essential for the acquisition of the osteoblast phenotype in early development. Although reports indicate p38 signalling plays a role in early skeletal development, its specific contributions to adult bone remodelling are still to be clarified.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated osteoblast-specific deletion of p38α to determine its significance in early skeletogenesis, as well as for bone homeostasis in adult skeleton. Early p38α deletion resulted in defective intramembranous and endochondral ossification in both calvaria and long bones. Mutant mice showed reduction of trabecular bone volume in distal femurs, associated with low trabecular thickness. In addition, knockout mice also displayed decreased femoral cortical bone volume and thickness. Deletion of p38α did not affect osteoclast function. Yet it impaired osteoblastogenesis and osteoblast maturation and activity through decreased expression of osteoblast-specific transcription factors and their targets. Furthermore, the inducible Cre system allowed us to control the onset of p38α disruption after birth by removal of doxycycline. Deletion of p38α at three or eight weeks postnatally led to significantly lower trabecular and cortical bone volume after 6 or 12 months.

CONCLUSIONS

Our data demonstrates that, in addition to early skeletogenesis, p38α is essential for osteoblasts to maintain their function in mineralized adult bone, as bone anabolism should be sustained throughout life. Moreover, our data also emphasizes that clinical development of p38 inhibitors should take into account their potential bone effects.

Stem cell factor induces AP-1-dependent mast cell IL-6 production via MAPK kinase 3 activity

Mast cells are critical immune effectors abundant in tissues interfacing with the environment and have major roles in allergen-induced inflammation and host responses to infection. SCF is a regulator of mast cell function and growth. However, the critical mechanisms in SCF-directed events remain incompletely defined. Here, we have investigated the role of MKK3 in mast cell SCF signaling-dependent functions by using BMMCs from MKK3-deficient mice. MKK3 was phosphorylated rapidly and persistently following SCF-induced activation and contributed to mast cell proliferation but not survival or migration in response to SCF. Analysis of SCF-induced mast cell mediator secretion demonstrated that IL-6 production is specifically dependent on MKK3 signals, both independently and in concert with IgE. Analysis of SCF-induced signaling showed that sustained p38 phosphorylation was impaired in MKK3-deficient mast cells, where as early JNK and IκBα activation were enhanced. Notably, SCF-inducible expression and activation of c-Jun, a component of the AP-1 transcription factor, was significantly dependent on MKK3. Accordingly, AP-1 DNA-binding activity and interaction with the IL6 gene promoter was markedly impaired in MKK3-deficient mast cells, whereas transcription factors of the Egr family, NF-κB, and NFAT retained near-full activity. These results designate MKK3 as a novel, positive regulator of SCF-induced mast cell proliferation and a critical signaling protein for AP-1-dependent IL-6 production.

EGCG attenuates pro-inflammatory cytokines and chemokines production in LPS-stimulated L02 hepatocyte

Endotoxin lipopolysaccharide (LPS) plays an important role in the acceleration of inflammatory reaction of hepatitis as the second attack. Compounds that can prevent inflammation by targeting LPS have potential therapeutic clinical application. Epigallocatechin-3-gallate (EGCG) has potent hepatocyte-protective effect and mild anti-hepatitis virus function. Here, we investigated whether EGCG attenuated the severity of inflammatory response in LPS-stimulated L02 hepatocytes. L02 hepatocytes were pretreated with EGCG for 2 h, then stimulated by LPS at 250 ng/ml. The expression levels of chemokine regulated upon activation normal T-cell expressed and secreted (Rantes) and monocyte chemotactic protein-1 (MCP-1), pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ, adhesion molecule intercellular adhesion molecule-1 (ICAM-1), oxidant stress molecules nitric oxide (NO), vascular endothelial growth factor (VEGF), and matrix metalloproteinase-2 (MMP-2) were tested by enzyme-linked immunosorbent assay. The expression of total extracellular signal-regulated kinase 1/2 (ERK1/2), phospho-ERK1/2 (p-ERK1/2), p-AKT, total p38, phospho-p38 (p-p38), total p65 and phospho-p65 (p-p65), IκBα, phospho-IκBα (p-IκBα) and TNF receptor associated factor 2 were tested by western blot analysis. Our results showed that pre-treatment with EGCG could significantly reduce the production of TNF-α, Rantes, MCP-1, ICAM-1, NO, VEGF, and MMP-2 in LPS-stimulated L02 hepatocytes in a dose-dependent manner. The effect of EGCG may be related to the inhibition of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways by down-regulation of p-IκBα, p65, p-p65, p-p38, p-ERK1/2, and p-AKT. These results indicate that EGCG suppresses LPS-induced inflammatory response and oxidant stress and exerts its hepatocyte-protective activity partially by inhibiting NF-κB and MAPK pathways.

p38 MAPK: a dual role in hepatocyte proliferation through reactive oxygen species

p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depending on the activation stimulus. The interplay between cell proliferation, p38 MAPK activation, and ROS production plays an important role in hepatocytes. In fact, low levels of ROS seem to be needed to activate several signaling pathways in response to hepatectomy and to orchestrate liver regeneration. p38 MAPK works as a sensor of oxidative stress and cells that have developed mechanisms to uncouple p38 MAPK activation from oxidative stress are more likely to become tumorigenic. So far, p38α influences the redox balance, determining cell survival, terminal differentiation, proliferation, and senescence. Further studies would be necessary in order to clarify the precise role of p38 MAPK signaling as a redox therapeutical target.

Tuning of protein kinase circuitry by p38α is vital for epithelial tissue homeostasis

The epithelium of mucosal and skin surfaces serves as a permeability barrier and affords mechanisms for local immune defense. Crucial to the development and maintenance of a properly functioning epithelium is the balance of cell proliferation, differentiation, and death. Here we show that this balance depends on cross-regulatory interactions among multiple protein kinase-mediated signals and their coordinated transmission. From an investigation of conditional gene knock-out mice, we find that epithelial-specific loss of the protein kinase p38α leads to aberrant activation of TAK1, JNK, EGF receptor, and ERK in distinct microanatomical areas of the intestines and skin. Consequently, the epithelial tissues display excessive proliferation, inadequate differentiation, and sensitivity to apoptosis. These anomalies leave the tissue prone to damage and collapse at the trigger of an environmental insult. The vulnerability of p38α-deficient epithelium predicts adverse effects of long term pharmacological p38α inhibition; yet such limitations could be overcome by concomitant blockade of one or more of the dysregulated protein kinase signaling pathways.

The p38α MAPK regulates microglial responsiveness to diffuse traumatic brain injury

Neuropathology after traumatic brain injury (TBI) is the result of both the immediate impact injury and secondary injury mechanisms. Unresolved post-traumatic glial activation is a secondary injury mechanism that contributes to a chronic state of neuroinflammation in both animal models of TBI and human head injury patients. We recently demonstrated, using in vitro models, that p38α MAPK signaling in microglia is a key event in promoting cytokine production in response to diverse disease-relevant stressors and subsequent inflammatory neuronal dysfunction. From these findings, we hypothesized that the p38α signaling pathway in microglia could be contributing to the secondary neuropathologic sequelae after a diffuse TBI. Mice where microglia were p38α-deficient (p38α KO) were protected against TBI-induced motor deficits and synaptic protein loss. In wild-type (WT) mice, diffuse TBI produced microglia morphological activation that lasted for at least 7 d; however, p38α KO mice failed to activate this response. Unexpectedly, we found that the peak of the early, acute phase cytokine and chemokine levels was increased in injured p38α KO mice compared with injured WT mice. The increased cytokine levels in the p38α KO mice could not be accounted for by more infiltration of macrophages or neutrophils, or increased astrogliosis. By 7 d after injury, the cytokine and chemokine levels remained elevated in injured WT mice but not in p38α KO mice. Together, these data suggest that p38α balances the inflammatory response by acutely attenuating the early proinflammatory cytokine surge while perpetuating the chronic microglia activation after TBI.