Peroxisome proliferator-activated receptor gamma negatively regulates IFN-beta production in Toll-like receptor (TLR) 3- and TLR4-stimulated macrophages by preventing interferon regulatory factor 3 binding to the IFN-beta promoter

Effect of eicosapentaenoic acid on innate immune responses in Atlantic salmon cells infected with infectious salmon anemia virus

Aquaculture is one of the world's fastest-growing sectors in food production but with multiple challenges related to animal handling and infections. The disease caused by infectious salmon anemia virus (ISAV) leads to outbreaks of local epidemics, reducing animal welfare, and causing significant economic losses. The composition of feed has shifted from marine ingredients such as fish oil and fish meal towards a more plant-based diet causing reduced levels of eicosapentaenoic acid (EPA). The aim of this study was to investigate whether low or high levels of EPA affect the expression of genes related to the innate immune response 48 h after infection with ISAV. The study includes seven experimental groups: ± ISAV and various levels of EPA up to 200 µM. Analysis of RNA sequencing data showed that more than 3000 genes were affected by ISAV alone (without additional EPA). In cells with increasing levels of EPA, more than 2500 additional genes were differentially expressed. This indicates that high levels of EPA concentration have an independent effect on gene expression in virus-infected cells, not observed at lower levels of EPA. Analyses of enriched biological processes and molecular functions (GO and KEGG analysis) revealed that EPA had a limited impact on the innate immune system alone, but that many processes were affected by EPA when cells were virus infected. Several biological pathways were affected, including protein synthesis (ribosomal transcripts), peroxisome proliferator activated receptor (PPAR) signaling, and ferroptosis. Cells exposed to both increasing concentrations of EPA and virus displayed gene expression patterns indicating increased formation of oxygen radicals and that cell death via ferroptosis was activated. This gene expression pattern was not observed during infection at low EPA levels or when Atlantic salmon kidney (ASK) cells were exposed to the highest EPA level (200 μM) without virus infection. Cell death via ferroptosis may therefore be a mechanism for controlled cell death and thus reduction of virus replication when there are enough polyunsaturated fatty acids (PUFAs) in the membrane.

Endocannabinoid 2-Arachidonoylglycerol Synthesis and Metabolism at Neuronal Nuclear Matrix Fractions Derived from Adult Rat Brain Cortex

In this report, we describe the kinetics characteristics of the diacylglycerol lipase-α (DGLα) located at the nuclear matrix of nuclei derived from adult cortical neurons. Thus, using high-resolution fluorescence microscopy, classical biochemical subcellular fractionation, and Western blot techniques, we demonstrate that the DGLα enzyme is located in the matrix of neuronal nuclei. Furthermore, by quantifying the 2-arachidonoylglycerol (2-AG) level by liquid chromatography and mass spectrometry when 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) was exogenously added as substrate, we describe the presence of a mechanism for 2-AG production through DGLα dependent biosynthesis with an apparent K_m (K_m^app) of 180 µM and a V_max of 1.3 pmol min^-1 µg^-1 protein. We also examined the presence of enzymes with hydrolytic and oxygenase activities that are able to use 2-AG as substrate, and described the localization and compartmentalization of the major 2-AG degradation enzymes, namely monoacylglycerol lipase (MGL), fatty acid amide hydrolase (FAAH), α/β-hydrolase domain 12 protein (ABHD12) and cyclooxygenase-2 (COX2). Of these, only ABHD12 exhibited the same distribution with respect to chromatin, lamin B1, SC-35 and NeuN as that described for DGLα. When 2-AG was exogenously added, we observed the production of arachidonic acid (AA), which was prevented by inhibitors (but not specific MGL or ABHD6 inhibitors) of the ABHD family. Overall, our results expand knowledge about the subcellular distribution of neuronal DGLα, and provide biochemical and morphological evidence to ensure that 2-AG is produced in the neuronal nuclear matrix. Thus, this work paves the way for proposing a working hypothesis about the role of 2-AG produced in neuronal nuclei.

PPARs and the Kynurenine Pathway in Melanoma-Potential Biological Interactions

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in various physiological and pathological processes within the skin. PPARs regulate several processes in one of the most aggressive skin cancers, melanoma, including proliferation, cell cycle, metabolic homeostasis, cell death, and metastasis. In this review, we focused not only on the biological activity of PPAR isoforms in melanoma initiation, progression, and metastasis but also on potential biological interactions between the PPAR signaling and the kynurenine pathways. The kynurenine pathway is a major pathway of tryptophan metabolism leading to nicotinamide adenine dinucleotide (NAD+) production. Importantly, various tryptophan metabolites exert biological activity toward cancer cells, including melanoma. Previous studies confirmed the functional relationship between PPAR and the kynurenine pathway in skeletal muscles. Despite the fact this interaction has not been reported in melanoma to date, some bioinformatics data and biological activity of PPAR ligands and tryptophan metabolites may suggest a potential involvement of these metabolic and signaling pathways in melanoma initiation, progression, and metastasis. Importantly, the possible relationship between the PPAR signaling pathway and the kynurenine pathway may relate not only to the direct biological effect on melanoma cells but also to the tumor microenvironment and the immune system.

Amplified Gliosis and Interferon-Associated Inflammation in the Aging Brain following Diffuse Traumatic Brain Injury

Traumatic brain injury (TBI) is associated with chronic psychiatric complications and increased risk for development of neurodegenerative pathology. Aged individuals account for most TBI-related hospitalizations and deaths. Nonetheless, neurobiological mechanisms that underlie worsened functional outcomes after TBI in the elderly remain unclear. Therefore, this study aimed to identify pathways that govern differential responses to TBI with age. Here, adult (2 months of age) and aged (16-18 months of age) male C57BL/6 mice were subjected to diffuse brain injury (midline fluid percussion), and cognition, gliosis, and neuroinflammation were determined 7 or 30 d postinjury (dpi). Cognitive impairment was evident 7 dpi, independent of age. There was enhanced morphologic restructuring of microglia and astrocytes 7 dpi in the cortex and hippocampus of aged mice compared with adults. Transcriptional analysis revealed robust age-dependent amplification of cytokine/chemokine, complement, innate immune, and interferon-associated inflammatory gene expression in the cortex 7 dpi. Ingenuity pathway analysis of the transcriptional data showed that type I interferon (IFN) signaling was significantly enhanced in the aged brain after TBI compared with adults. Age prolonged inflammatory signaling and microgliosis 30 dpi with an increased presence of rod microglia. Based on these results, a STING (stimulator of interferon genes) agonist, DMXAA, was used to determine whether augmenting IFN signaling worsened cortical inflammation and gliosis after TBI. DMXAA-treated Adult-TBI mice showed comparable expression of myriad genes that were overexpressed in the cortex of Aged-TBI mice, including Irf7, Clec7a, Cxcl10, and Ccl5 Overall, diffuse TBI promoted amplified IFN signaling in aged mice, resulting in extended inflammation and gliosis.SIGNIFICANCE STATEMENT Elderly individuals are at higher risk of complications following traumatic brain injury (TBI). Individuals >70 years old have the highest rates of TBI-related hospitalization, neurodegenerative pathology, and death. Although inflammation has been linked with poor outcomes in aging, the specific biological pathways driving worsened outcomes after TBI in aging remain undefined. In this study, we identify amplified interferon-associated inflammation and gliosis in aged mice following TBI that was associated with persistent inflammatory gene expression and microglial morphologic diversity 30 dpi. STING (stimulator of interferon genes) agonist DMXAA was used to demonstrate a causal link between augmented interferon signaling and worsened neuroinflammation after TBI. Therefore, interferon signaling may represent a therapeutic target to reduce inflammation-associated complications following TBI.

Protection against influenza-induced Acute Lung Injury (ALI) by enhanced induction of M2a macrophages: possible role of PPARγ/RXR ligands in IL-4-induced M2a macrophage differentiation

Many respiratory viruses cause lung damage that may evolve into acute lung injury (ALI), a cytokine storm, acute respiratory distress syndrome, and ultimately, death. Peroxisome proliferator activated receptor gamma (PPARγ), a member of the nuclear hormone receptor (NHR) family of transcription factors, regulates transcription by forming heterodimers with another NHR family member, Retinoid X Receptor (RXR). Each component of the heterodimer binds specific ligands that modify transcriptional capacity of the entire heterodimer by recruiting different co-activators/co-repressors. However, the role of PPARγ/RXR ligands in the context of influenza infection is not well understood. PPARγ is associated with macrophage differentiation to an anti-inflammatory M2 state. We show that mice lacking the IL-4Rα receptor, required for M2a macrophage differentiation, are more susceptible to mouse-adapted influenza (A/PR/8/34; "PR8")-induced lethality. Mice lacking Ptgs2, that encodes COX-2, a key proinflammatory M1 macrophage mediator, are more resistant. Blocking the receptor for COX-2-induced Prostaglandin E2 (PGE2) was also protective. Treatment with pioglitazone (PGZ), a PPARγ ligand, increased survival from PR8 infection, decreased M1 macrophage gene expression, and increased PPARγ mRNA in lungs. Conversely, conditional knockout mice expressing PPARγ-deficient macrophages were significantly more sensitive to PR8-induced lethality. These findings were extended in cotton rats: PGZ blunted lung inflammation and M1 cytokine gene expression after challenge with non-adapted human influenza. To study mechanisms by which PPARγ/RXR transcription factors induce canonical M2a genes, WT mouse macrophages were treated with IL-4 in the absence or presence of rosiglitazone (RGZ; PPARγ ligand), LG100754 (LG; RXR ligand), or both. IL-4 dose-dependently induced M2a genes Arg1, Mrc1, Chil3, and Retnla. Treatment of macrophages with IL-4 and RGZ and/or LG differentially affected induction of Arg1 and Mrc1 vs. Chil3 and Retnla gene expression. In PPARγ-deficient macrophages, IL-4 alone failed to induce Arg1 and Mrc1 gene expression; however, concurrent treatment with LG or RGZ + LG enhanced IL-4-induced Arg1 and Mrc1 expression, but to a lower level than in WT macrophages, findings confirmed in the murine alveolar macrophage cell line, MH-S. These findings support a model in which PPARγ/RXR heterodimers control IL-4-induced M2a differentiation, and suggest that PPARγ/RXR agonists should be considered as important tools for clinical intervention against influenza-induced ALI.

Regulation of adipogenic differentiation and adipose tissue inflammation by interferon regulatory factor 3

Dysfunction of adipocytes and adipose tissue is a primary defect in obesity and obesity-associated metabolic diseases. Interferon regulatory factor 3 (IRF3) has been implicated in adipogenesis. However, the role of IRF3 in obesity and obesity-associated disorders remains unclear. Here, we show that IRF3 expression in human adipose tissues is positively associated with insulin sensitivity and negatively associated with type 2 diabetes. In mouse pre-adipocytes, deficiency of IRF3 results in increased expression of PPARγ and PPARγ-mediated adipogenic genes, leading to increased adipogenesis and altered adipocyte functionality. The IRF3 knockout (KO) mice develop obesity, insulin resistance, glucose intolerance, and eventually type 2 diabetes with aging, which is associated with the development of white adipose tissue (WAT) inflammation. Increased macrophage accumulation with M1 phenotype which is due to the loss of IFNβ-mediated IL-10 expression is observed in WAT of the KO mice compared to that in wild-type mice. Bone-marrow reconstitution experiments demonstrate that the nonhematopoietic cells are the primary contributors to the development of obesity and both hematopoietic and nonhematopoietic cells contribute to the development of obesity-related complications in IRF3 KO mice. This study demonstrates that IRF3 regulates the biology of multiple cell types including adipocytes and macrophages to prevent the development of obesity and obesity-related complications and hence, could be a potential target for therapeutic interventions for the prevention and treatment of obesity-associated metabolic disorders.

Development of mode of action networks related to the potential role of PPARγ in respiratory diseases

The peroxisome proliferator-activated receptor γ (PPARγ) is a key transcription factor, operating at the intercept of metabolic control and immunomodulation. It is ubiquitously expressed in multiple tissues and organs, including lungs. There is a growing body of information supporting the role of PPARγ signalling in respiratory diseases. The aim of the present study was to develop mode of action (MoA) networks reflecting the relationships between PPARγ signalling and the progression/alleviation of a spectrum of lung pathologies. Data mining was performed using the resources of the NIH PubMed and PubChem information systems. By linking available data on pathological/therapeutic effects of PPARγ modulation, knowledge-based MoA networking at different levels of biological organization (molecular, cellular, tissue, organ, and system) was performed. Multiple MoA networks were developed to relate PPARγ modulation to the progress or the alleviation of pulmonary disorders, triggered by diverse pathogenic, genetic, chemical, or mechanical factors. Pharmacological targeting of PPARγ signalling was discussed with regard to ligand- and cell type-specific effects in the context of distinct disease inductor- and disease stage-dependent patterns. The proposed MoA networking analysis allows for a better understanding of the potential role of PPARγ modulation in lung pathologies. It presents a mechanistically justified basis for further computational, experimental, and clinical monitoring studies on the dynamic control of PPARγ signalling in respiratory diseases.

A novel ACE2 isoform is expressed in human respiratory epithelia and is upregulated in response to interferons and RNA respiratory virus infection

Angiotensin-converting enzyme 2 (ACE2) is the main entry point in airway epithelial cells for SARS-CoV-2. ACE2 binding to the SARS-CoV-2 protein spike triggers viral fusion with the cell plasma membrane, resulting in viral RNA genome delivery into the host. Despite ACE2's critical role in SARS-CoV-2 infection, full understanding of ACE2 expression, including in response to viral infection, remains unclear. ACE2 was thought to encode five transcripts and one protein of 805 amino acids. In the present study, we identify a novel short isoform of ACE2 expressed in the airway epithelium, the main site of SARS-CoV-2 infection. Short ACE2 is substantially upregulated in response to interferon stimulation and rhinovirus infection, but not SARS-CoV-2 infection. This short isoform lacks SARS-CoV-2 spike high-affinity binding sites and, altogether, our data are consistent with a model where short ACE2 is unlikely to directly contribute to host susceptibility to SARS-CoV-2 infection.

Changes in H3K27ac at Gene Regulatory Regions in Porcine Alveolar Macrophages Following LPS or PolyIC Exposure

Changes in chromatin structure, especially in histone modifications (HMs), linked with chromatin accessibility for transcription machinery, are considered to play significant roles in transcriptional regulation. Alveolar macrophages (AM) are important immune cells for protection against pulmonary pathogens, and must readily respond to bacteria and viruses that enter the airways. Mechanism(s) controlling AM innate response to different pathogen-associated molecular patterns (PAMPs) are not well defined in pigs. By combining RNA sequencing (RNA-seq) with chromatin immunoprecipitation and sequencing (ChIP-seq) for four histone marks (H3K4me3, H3K4me1, H3K27ac and H3K27me3), we established a chromatin state map for AM stimulated with two different PAMPs, lipopolysaccharide (LPS) and Poly(I:C), and investigated the potential effect of identified histone modifications on transcription factor binding motif (TFBM) prediction and RNA abundance changes in these AM. The integrative analysis suggests that the differential gene expression between non-stimulated and stimulated AM is significantly associated with changes in the H3K27ac level at active regulatory regions. Although global changes in chromatin states were minor after stimulation, we detected chromatin state changes for differentially expressed genes involved in the TLR4, TLR3 and RIG-I signaling pathways. We found that regions marked by H3K27ac genome-wide were enriched for TFBMs of TF that are involved in the inflammatory response. We further documented that TF whose expression was induced by these stimuli had TFBMs enriched within H3K27ac-marked regions whose chromatin state changed by these same stimuli. Given that the dramatic transcriptomic changes and minor chromatin state changes occurred in response to both stimuli, we conclude that regulatory elements (i.e. active promoters) that contain transcription factor binding motifs were already active/poised in AM for immediate inflammatory response to PAMPs. In summary, our data provides the first chromatin state map of porcine AM in response to bacterial and viral PAMPs, contributing to the Functional Annotation of Animal Genomes (FAANG) project, and demonstrates the role of HMs, especially H3K27ac, in regulating transcription in AM in response to LPS and Poly(I:C).

Pollen exposure weakens innate defense against respiratory viruses

BACKGROUND

Hundreds of plant species release their pollen into the air every year during early spring. During that period, pollen allergic as well as non-allergic patients frequently present to doctors with severe respiratory tract infections. Our objective was therefore to assess whether pollen may interfere with antiviral immunity.

METHODS

We combined data from real-life human exposure cohorts, a mouse model and human cell culture to test our hypothesis.

RESULTS

Pollen significantly diminished interferon-λ and pro-inflammatory chemokine responses of airway epithelia to rhinovirus and viral mimics and decreased nuclear translocation of interferon regulatory factors. In mice infected with respiratory syncytial virus, co-exposure to pollen caused attenuated antiviral gene expression and increased pulmonary viral titers. In non-allergic human volunteers, nasal symptoms were positively correlated with airborne birch pollen abundance, and nasal birch pollen challenge led to downregulation of type I and -III interferons in nasal mucosa. In a large patient cohort, numbers of rhinoviruspositive cases were correlated with airborne birch pollen concentrations.

CONCLUSION

The ability of pollen to suppress innate antiviral immunity, independent of allergy, suggests that high-risk population groups should avoid extensive outdoor activities when pollen and respiratory virus seasons coincide.

Interferon Regulatory Factor 3 Deficiency Induces Age-Related Alterations of the Retina in Young and Old Mice

Age-related changes in visual function and retina structure are very common in aged animals, but the underlying mechanisms of these changes remain unclear. Here we report that the expression of interferon regulatory factor 3 (IRF3), a critical immune regulatory factor, is dramatically down-regulated in mouse retinas during aging. To address the role of IRF3 in the retina, we examined the structure and function of retinas in young (3–4 months) and old (22–24 months) Irf3^-/- mice in comparison to age-matched wildtype (WT) mice. We found that IRF3 deletion resulted in impaired electroretinogram (ERG) responses and decreased retinal thickness in both young and old mice. In addition, numerous synapses of the outer plexiform layer (OPL) were found obviously extending into outer nuclear layer (ONL) in Irf3^-/- mice, along with a reduction of the average synapse density in the OPL. These changes suggest that IRF3 deletion may accelerate retinal senescence. In support of this hypothesis, a number of classic senescence-associated markers were found in remarkably elevated level in Irf3^-/- retina, including p53, p16^INK4a, inositol-requiring enzyme 1α (IREα), p-H2A.X and promyelocytic leukemia protein (PML). Overall, our results indicate that maintenance normal IRF3 levels is necessary for retinal structure and function and suggest that IRF3 is an important regulator of retinal senescence.

The effect of fenofibrate, a PPARα activator on toll-like receptor-4 signal transduction in melanoma both in vitro and in vivo

BACKGROUND

The anti-cancer effect of peroxisome proliferator-activated receptor (PPAR) α ligands on growth and metastatic potential of melanoma cells has been shown previously. However, the mechanism underlying these effects remains to be elucidated. Here, we investigated the effects of fenofibrate (PPAR ligand) on Toll-like receptor-4 (TLR-4) signaling in mice melanoma.

METHODS

Mice melanoma cells (B16F10) were treated with fenofibrate or LPS or LPS + fenofibrate or pre-treated with CLI-095 (a TLR4 inhibitor), followed by fenofibrate. In in vivo model, C57BL/6 mice were subcutaneously injected with B16F10 cells (with/without LPS pre-treatment), and fenofibrate was administrated after development of palpable tumors. Cell proliferation, the expression level of Tlr4, Myd88, Nf-κb1 genes, TLR-4 protein expression, TNF-α levels, and tumor volume were measured.

RESULT

Our results indicated that fenofibrate significantly inhibited the Tlr-4, Myd-88, and Nf-kb1 mRNA expression and TNF-α concentration in B16F10 LPS-stimulated cells. In addition, blocking TLR-4 signaling increased the anti-inflammatory potential of fenofibrate. Also fenofibrate can reduce LPS-induced tumor volume, Tlr-4, Myd-88, Nf-kb1 mRNA, and TLR-4 protein expression in tumor tissue and also TNF-α level in tumor tissue lysate.

CONCLUSION

Our data indicate that fenofibrate may exert its anti-melanoma effects via interaction with TLR4-dependent signaling pathway (TLR-4/MyD-88/ NF-kB).

Peroxisome Proliferator-Activated Receptor Gamma (PPAR) Suppresses Inflammation and Bacterial Clearance during Influenza-Bacterial Super-Infection

Influenza virus is among the most common causes of respiratory illness worldwide and can be complicated by secondary bacterial pneumonia, a frequent cause of mortality. When influenza virus infects the lung, the innate immune response is activated, and interferons and inflammatory mediators are released. This "cytokine storm" is thought to play a role in influenza-induced lung pathogenesis. Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the nuclear hormone receptor super-family. PPARγ has numerous functions including enhancing lipid and glucose metabolism and cellular differentiation and suppressing inflammation. Synthetic PPARγagonists (thiazolidinediones or glitazones) have been used clinically in the treatment of type II diabetes. Using data from the National Health and Nutrition Examination Survey (NHANES), diabetic participants taking rosiglitazone had an increased risk of mortality from influenza/pneumonia compared to those not taking the drug. We examined the effect of rosiglitazone treatment during influenza and secondary bacterial (Methicillin resistant Staphylococcus aureus) pneumonia in mice. We found decreased influenza viral burden, decreased numbers of neutrophils and macrophages in bronchoalveolar lavage, and decreased production of cytokines and chemokines in influenza infected, rosiglitazone-treated mice when compared to controls. However, rosiglitazone treatment compromised bacterial clearance during influenza-bacterial super-infection. Both human and mouse data suggest that rosiglitazone treatment worsens the outcome of influenza-associated pneumonia.

4-Methylcoumarin-[5,6-g]-hesperetin attenuates inflammatory responses in alcoholic hepatitis through PPAR-γ activation

4-Methylcoumarin-[5,6-g]-hesperetin (4-MCH) is a hesperidin derivative produced by the structural modification of hesperetin. Alcoholic hepatitis (AH) is the origin of many serious liver diseases that are accompanied by hepatic inflammation. In this study, we detected the anti-inflammatory activity of 4-MCH in EtOH fed mice and examined the potential molecular mechanism of this activity. We found that 4-MCH suppressed the release of inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in primary liver macrophages isolated from mice and in EtOH-treated RAW264.7 cells. In addition, we showed that the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) was down-regulated in vivo and in vitro in AH. Furthermore, 4-MCH acted as an activator of PPAR-γ, which could therefore ameliorate the inhibitory effects of EtOH on the expression of PPAR-γ. The impairment of PPAR-γ function (T0070907 or PPAR-γ siRNA treatment) resulted in greater inflammation than that in the control group. Conversely, over-expression of PPAR-γ further reduced the release of inflammatory cytokines from EtOH-stimulated RAW264.7 cells. Additional investigations showed that 4-MCH significantly inhibited the phosphorylation of p65. Collectively, these results indicate that 4-MCH alleviated the inflammatory reaction through PPAR-γ activation via the NF-κB-p65 signaling pathway, which regulates the expression of IL-6 and TNF-α in AH.

Crosstalk between Peroxisome Proliferator-Activated Receptors and Toll-Like Receptors: A Systematic Review

As one of the four major families of pattern recognition receptors (PRRs), toll like receptors (TLRs) are crucial and important components of the innate immune system. Peroxisome proliferatoractivated receptors (PPARs) with three isoforms are transcription factors classified as a subfamily of nuclear receptor proteins, and are of significant regulatory activity in cellular differentiation, development, metabolism, and tumorigenesis. It is well established that PPARs agonists display anti-inflammatory effects through inhibition of the nuclear factor-kappa B (NF-κB) pathway, a key regulator of immune and inflammatory responses, in a sense that TLRs signaling pathways are mainly toward activation of NF-κB. Through a systematic review of previous studies, we aimed to address and clarify the reciprocal interaction between TLRs and PPARs in hope to find alternative therapeutic approaches for inflammatory diseases. Among the available scientific database, 31 articles were selected for this review. A comprehensive review of this database confirms the presence of a cross-talk between PPARs and TLRs, indicating that not only PPARs stimulation may affect the expression level of TLRs via several mechanisms leading to modulating TLRs activities, but also TLRs have the potential to moderate the expression of PPARs. We, therefore, conclude that, as a key regulator of the innate immune system, the interaction between PPARs and TLRs is a potential therapeutic target in disease treatment.

Paeonol attenuates ligation-induced periodontitis in rats by inhibiting osteoclastogenesis via regulating Nrf2/NF-κB/NFATc1 signaling pathway

Paeonol is a natural phenolic compound in Moutan Cortex with multiple biological functions, such as anti-inflammatory and anti-oxidant activity. Recent evidence has proven that persistent inflammation, oxidative stress, along with nuclear factor E2-related factor 2 (Nrf2) signaling dysfunction in periodontium are the possible causes of alveolar bone resorption, and ultimately lead to periodontitis. The present study was designed to explore the protective effects of paeonol on ligation-induced periodontitis in rats, and investigate the possible mechanism. We found that treatment with paeonol (40, 80 mg/kg, intraperitoneal injection) for 7 days remarkably decreased the expression of receptor activator of nuclear factor kappa-B ligand increased the expression of osteoprotegrin and inhibited the formation of osteoclasts. This function of paeonol might be correlated with its ability to reduce inflammatory factors (IL-1β, IL-6 and TNF-α) and alleviate oxidative stress (SOD, MDA, GSH and ROS) in gingival tissues. Besides, paeonol increased Nrf2 activity. Silence of Nrf2 using specific siRNA diminished the inhibitory effect of paeonol on NF-κB p65 activation and downstream expression, suggesting that Nrf2 was essential for protective effect of paeonol. These results showed that paeonol protected against periodontitis-aggravated osteoclastogenesis and alveolar bone lesion via regulating Nrf2/NF-κB/NFATc1 signaling pathway.

PPARγ Deficiency Suppresses the Release of IL-1β and IL-1α in Macrophages via a Type 1 IFN-Dependent Mechanism

Obesity and diabetes modulate macrophage activation, often leading to prolonged inflammation and dysfunctional tissue repair. Increasing evidence suggests that the NLRP3 inflammasome plays an important role in obesity-associated inflammation. We have previously shown that activation of the lipotoxic inflammasome by excess fatty acids in macrophages occurs via a lysosome-dependent pathway. However, the mechanisms that link cellular lipid metabolism to altered inflammation remain poorly understood. PPARγ is a nuclear receptor transcription factor expressed by macrophages that is known to alter lipid handling, mitochondrial function, and inflammatory cytokine expression. To undercover novel links between metabolic signaling and lipotoxic inflammasome activation, we investigated mouse primary macrophages deficient in PPARγ. Contrary to our expectation, PPARγ knockout (KO) macrophages released significantly less IL-1β and IL-1α in response to lipotoxic stimulation. The suppression occurred at the transcriptional level and was apparent for multiple activators of the NLRP3 inflammasome. RNA sequencing revealed upregulation of IFN-β in activated PPARγKO macrophages, and this was confirmed at the protein level. A blocking Ab against the type 1 IFNR restored the release of IL-1β to wild type levels in PPARγKO cells, confirming the mechanistic link between these events. Conversely, PPARγ activation with rosiglitazone selectively suppressed IFN-β expression in activated macrophages. Loss of PPARγ also resulted in diminished expression of genes involved in sterol biosynthesis, a pathway known to influence IFN production. Together, these findings demonstrate a cross-talk pathway that influences the interplay between metabolism and inflammation in macrophages.

Regulator of calcineurin 1 differentially regulates TLR-dependent MyD88 and TRIF signaling pathways

Toll-like receptors (TLRs) recognize the conserved molecular patterns in microorganisms and trigger myeloid differentiation primary response 88 (MyD88) and/or TIR-domain-containing adapter-inducing interferon-β (TRIF) pathways that are critical for host defense against microbial infection. However, the molecular mechanisms that govern TLR signaling remain incompletely understood. Regulator of calcineurin-1 (RCAN1), a small evolutionarily conserved protein that inhibits calcineurin phosphatase activity, suppresses inflammation during Pseudomonas aeruginosa infection. Here, we define the roles for RCAN1 in P. aeruginosa lipopolysaccharide (LPS)-activated TLR4 signaling. We compared the effects of P. aeruginosa LPS challenge on bone marrow-derived macrophages from both wild-type and RCAN1-deficient mice and found that RCAN1 deficiency increased the MyD88-NF-κB-mediated cytokine production (IL-6, TNF and MIP-2), whereas TRIF-interferon-stimulated response elements (ISRE)-mediated cytokine production (IFNβ, RANTES and IP-10) was suppressed. RCAN1 deficiency caused increased IκBα phosphorylation and NF-κB activity in the MyD88-dependent pathway, but impaired ISRE activation and reduced IRF7 expression in the TRIF-dependent pathway. Complementary studies of a mouse model of P. aeruginosa LPS-induced acute pneumonia confirmed that RCAN1-deficient mice displayed greatly enhanced NF-κB activity and MyD88-NF-κB-mediated cytokine production, which correlated with enhanced pulmonary infiltration of neutrophils. By contrast, RCAN1 deficiency had little effect on the TRIF pathway in vivo. These findings demonstrate a novel regulatory role of RCAN1 in TLR signaling, which differentially regulates MyD88 and TRIF pathways.

BCL6 attenuates renal inflammation via negative regulation of NLRP3 transcription

Renal inflammation contributes to the pathogeneses of hypertension. This study was designed to determine whether B-cell lymphoma 6 (BCL6) attenuates renal NLRP3 inflammasome activation and inflammation and its underlying mechanism. Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were used in the present study. Angiotensin (Ang) II or lipopolysaccharides (LPS) was used to induce inflammation in HK-2 cells, a human renal tubular epithelial (RTE) cell line. NLRP3 inflammasome was activated and BCL6 was downregulated in the kidneys of SHR. Either Ang II or LPS suppressed BCL6 expression in HK-2 cells. BCL6 overexpression in HK-2 cells attenuated Ang II-induced NLRP3 upregulation, inflammation and cell injury. The inhibitory effects of BCL6 overexpression on NLRP3 expression and inflammation were also observed in LPS-treated HK-2 cells. BCL6 inhibited the NLRP3 transcription via binding to the NLRP3 promoter. BCL6 knockdown with shRNA increased NLRP3 and mature IL-1β expression levels in both PBS- or Ang II-treated HK-2 cells but had no significant effects on ASC, pro-caspase-1 and pro-IL-1β expression levels. BCL6 overexpression caused by recombinant lentivirus expressing BCL6 reduced blood pressure in SHR. BCL6 overexpression prevented the upregulation of NLRP3 and mature IL-1β expression levels in the renal cortex of SHR. The results indicate that BCL6 attenuates Ang II- or LPS-induced inflammation in HK-2 cells via negative regulation of NLRP3 transcription. BCL6 overexpression in SHR reduced blood pressure, NLRP3 expression and inflammation in the renal cortex of SHR.

Impaired anti-inflammatory activity of PPARγ in the salivary epithelia of Sjögren's syndrome patients imposed by intrinsic NF-κB activation

Sjögren's syndrome (SS) patients manifest inflammation in the salivary glands (SG) and evidence of persistent intrinsic activation of ductal SG epithelial cells (SGEC), demonstrable in non-neoplastic SGEC lines derived from patients (SS-SGEC). The peroxisome-proliferator-activated receptor-γ (PPARγ) mediates important anti-inflammatory activities in epithelial cells. Herein, the comparative analysis of SG biopsies and SGEC lines obtained from SS patients and controls had revealed constitutively reduced PPARγ expression, transcriptional activity and anti-inflammatory function in the ductal epithelia of SS patients that were associated with cell-autonomously activated NF-κB and IL-1β pathways. Transcriptome profiling analysis revealed several differentially expressed proinflammatory and metabolism-related gene sets in SS-SGEC lines. These aberrations largely correlated with the severity of histopathologic lesions, the disease activity and the occurrence of adverse manifestations in SS patients studied, a fact which corroborates the key role of the persistently-activated epithelia in the pathogenesis of both local and systemic features of this disease. The treatment of control SGEC lines with PPARγ agonists was found to diminish the NF-κB activation and apoptosis induced by proinflammatory agents. In addition, the in-vitro application of PPARγ agonists and pharmacologic inhibitors of IL-1β and NF-κB had significant beneficial effects on SS-SGEC lines, such as the restoration of PPARγ functions and the reduction of their intrinsic activation, a fact which may advocate the future clinical study of the above agents as therapeutic modalities for SS.

Toll-like Receptor 4 Signaling Pathway in the Protective Effect of Pioglitazone on Experimental Immunoglobulin A Nephropathy

Background:

In vitro experiments have revealed that toll-like receptor 4 (TLR4) pathway is involved in the progression of immunoglobulin A nephropathy (IgAN) by induction of proinflammatory cytokines. Evidence showed that, in other disease models, peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists have been shown to exert anti-inflammatory effects through suppression of the expression and activity of TLR4. However, the interaction between PPAR-γ and TLR4 in IgAN has not been fully studied both in vitro and in vivo. In this study, we explored whether TLR4 pathway attributed to the progression of IgAN in experimental rats.

Methods:

Bovine gamma globulin was used to establish IgAN model. Fifty-four Lewis rats were randomly divided into six groups: Control_TAK242, IgAN_TAK242, toll-like receptor 4 inhibitor (TAK242) groups (rats were administrated with TLR4 inhibitor, TAK242) and Control_Pio, IgAN_Pio, Pio groups (rats were administrated with PPAR-γ agonist, pioglitazone). Urinary albumin-to-creatinine ratio (ACR), serum creatinine, and blood urea nitrogen were detected by automatic biochemical analyzer. Renal histopathological changes were observed after hematoxylin-eosin staining, and the IgA deposition in glomeruli was measured by immunofluorescence staining. Real-time polymerase chain reaction and Western blotting were used to detect TLR4 and interleukin-1 beta (IL-1β) message ribonucleic acid (mRNA) and protein expression in renal tissues. Results were presented as mean ± standard deviation. Differences between groups were analyzed by one-way analysis of variance.

Results:

Compared to normal rats, experimental rats showed higher ACR (4.45 ± 1.33 mg/mmol vs. 2.89 ± 0.96 mg/mmol, P < 0.05), obvious IgA deposition with mesangial hypercellularity, hyperplasia of mesangial matrix accompanied by increased serum IL-1β (48.28 ± 13.49 pg/ml vs. 35.56 ± 7.41pg/ml, P < 0.05), and renal expression of IL-1β and TLR4. The biochemical parameters and renal pathological injury were relieved in both TAK242 group and Pio group. The expressions of renal tissue TLR4, IL-1β, and serum IL-1β were decreased in rats treated with TAK242, and the expression of TLR4 mRNA and protein was significantly reduced in Pio group compared to IgAN_Pio group (1.22 ± 0.28 vs. 1.72 ± 0.45, P < 0.01, and 0.12 ± 0.03 vs. 0.21 ± 0.05, P < 0.01).

Conclusions:

Our study proves that inflammation mediated by TLR4 signaling pathway is involved in the progression of IgAN in rat models. Moreover, pioglitazone can inhibit the expression of TLR4 in IgAN.

Oxidized Low-Density Lipoprotein Loading of Macrophages Downregulates TLR-Induced Proinflammatory Responses in a Gene-Specific and Temporal Manner through Transcriptional Control

Hypercholesterolemia is a key risk factor for atherosclerosis and leads to the uptake of native and oxidized low-density lipoprotein (oxLDL) by macrophages (Mϕs) and foam cell formation. Inflammatory processes accompany Mϕ foam cell formation in the artery wall, yet the relationship between Mϕ lipid loading and their response to inflammatory stimuli remains elusive. We investigated proinflammatory gene expression in thioglycollate-elicited peritoneal Mϕs, bone marrow-derived Mϕs and dendritic cells, and RAW264.7 cells. Loading with oxLDL did not induce peritoneal Mϕ apoptosis or modulate basal-level expression of proinflammatory genes. Upon stimulation of TLR4, the rapid induction of IFN-β was inhibited in cells loaded with oxLDL, whereas the induction of other proinflammatory genes by TLR4 (LPS), TLR3 (polyriboinosinic-polyribocytidylic acid), TLR2 (Pam₃CSK₄), and TLR9 (CpG) remained comparable within the first 2 h. Subsequently, the expression of a subset of proinflammatory genes (e.g., IL-1β, IL-6, CCL5) was reduced in oxLDL-loaded cells at the level of transcription. This phenomenon was partially dependent on NF erythroid 2-related factor 2 (NRF2) but not on nuclear liver X receptors α and β (LXRα,β), peroxisome proliferator-activated receptor-γ (PPARγ), and activating transcription factor 3 (ATF3). LPS-induced NF-κB reporter activity and intracellular signaling by NF-κB and MAPK pathways were comparable in oxLDL-loaded Mϕs, yet the binding of p65/RelA (the prototypic NF-κB family member) was reduced at IL-6 and CCL5 promoters. This study revealed that oxLDL loading of Mϕs negatively regulates transcription at late stages of TLR-induced proinflammatory gene expression and implicates epigenetic mechanisms such as histone deacetylase activity.

ERRα negatively regulates type I interferon induction by inhibiting TBK1-IRF3 interaction

Estrogen-related receptor α (ERRα) is a member of the nuclear receptor superfamily controlling energy homeostasis; however, its precise role in regulating antiviral innate immunity remains to be clarified. Here, we showed that ERRα deficiency conferred resistance to viral infection both in vivo and in vitro. Mechanistically, ERRα inhibited the production of type-I interferon (IFN-I) and the expression of multiple interferon-stimulated genes (ISGs). Furthermore, we found that viral infection induced TBK1-dependent ERRα stabilization, which in turn associated with TBK1 and IRF3 to impede the formation of TBK1-IRF3, IRF3 phosphorylation, IRF3 dimerization, and the DNA binding affinity of IRF3. The effect of ERRα on IFN-I production was independent of its transcriptional activity and PCG-1α. Notably, ERRα chemical inhibitor XCT790 has broad antiviral potency. This work not only identifies ERRα as a critical negative regulator of antiviral signaling, but also provides a potential target for future antiviral therapy.

The molecular mechanisms of action of PPAR-γ agonists in the treatment of corneal alkali burns (Review)

Corneal alkali burns (CAB) are characterized by injury-induced inflammation, fibrosis and neovascularization (NV), and may lead to blindness. This review evaluates the current knowledge of the molecular mechanisms responsible for CAB. The processes of cytokine production, chemotaxis, inflammatory responses, immune response, cell signal transduction, matrix metalloproteinase production and vascular factors in CAB are discussed. Previous evidence indicates that peroxisome proliferator-activated receptor γ (PPAR-γ) agonists suppress immune responses, inflammation, corneal fibrosis and NV. This review also discusses the role of PPAR-γ as an anti-inflammatory, anti-fibrotic and anti-angiogenic agent in the treatment of CAB, as well as the potential role of PPAR-γ in the pathological process of CAB. There have been numerous studies evaluating the clinical profiles of CAB, and the aim of this systematic review was to summarize the evidence regarding the treatment of CAB with PPAR-γ agonists.

Inhibition of tumor growth by a newly-identified activator for epidermal fatty acid binding protein

Our previous studies have demonstrated that expression of epidermal fatty acid binding protein (E-FABP) in tumor associated macrophages (TAMs) promotes macrophage anti-tumor activity by enhancing IFNβ responses in tumor models. Thus, E-FABP represents a new protective factor in enhancing tumor immune surveillance against tumor development. Herein, we report the compound 5-(benzylamino)-2-(3-methylphenyl)-1,3-oxazole-4-carbonitrile (designated EI-05) as a novel E-FABP activator for inhibition of mammary tumor growth. EI-05 was selected from the ZINC compound library using molecular docking analysis based on the crystal structure of E-FABP. Although EI-05 is unable to bind E-FABP directly, it significantly increases E-FABP expression in macrophages during inflammation. Stimulation of macrophages with EI-05 remarkably enhances lipid droplet formation and IFNβ production, which further promotes the anti-tumor activity of macrophages. Importantly, administering EI-05 in vivo significantly inhibits mammary tumor growth in a syngeneic mouse model. Altogether, these results suggest that EI-05 may represent a promising drug candidate for anti-tumor treatment through enhancing E-FABP activity and IFNβ responses in macrophages.

The role of pattern recognition receptors in the innate recognition of Candida albicans

Candida albicans is both a commensal microorganism in healthy individuals and a major fungal pathogen causing high mortality in immunocompromised patients. Yeast-hypha morphological transition is a well known virulence trait of C. albicans. Host innate immunity to C. albicans critically requires pattern recognition receptors (PRRs). In this review, we summarize the PRRs involved in the recognition of C. albicans in epithelial cells, endothelial cells, and phagocytic cells separately. We figure out the differential recognition of yeasts and hyphae, the findings on PRR-deficient mice, and the discoveries on human PRR-related single nucleotide polymorphisms (SNPs).

PPARγ ameliorated LPS induced inflammation of HEK cell line expressing both human Toll-like receptor 4 (TLR4) and MD2

TLR4 is transmembrane pattern-recognition receptor that initiates signals in response to diverse pathogen-associated molecular patterns especially LPS. Recently, there have been an increasing number of studies about the role of TLRs in the pathogenesis of several disorders as well as the therapeutic potential of TLR intervention in such diseases. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a ligand-activated transcription factor with numerous biological effects. PPARγ has been shown to exert a potential anti-inflammatory effect through suppression of TLR4-mediated inflammation. Therefore, PPARγ agonists may have a potential to combat inflammatory conditions in pathologic states. The current study aims to show the decrease of inflammation by overexpression of PPARγ in a cell reporter model. To reach this goal, recombinant pBudCE4.1 (+) containing encoding sequences of human TLR4 and MD2 was constructed and used to transfect HEK cells. Subsequently, inflammation was induced by LPS treatment as control group. In the treatment group, overexpression of PPARγ prior to inflammation was performed and the expression of inflammatory markers was assessed in this condition. The expression of inflammatory markers (TNFα and iNOS) was defined by quantitative real time PCR and the amount of phosphorylated NF-κB was measured by western blot. Data indicated expression of TNFα and iNOS increased in LPS induced inflammation of stably transformed HEK cells with MD2 and TLR4. In this cell reporter model overexpression of PPARγ dramatically prevented LPS-induced inflammation through the blocking of TLR4/NF-κB signaling. PPARγ was shown to negatively regulate TLR4 activity and therefore exerts its anti-inflammatory action against LPS induced inflammation.

PPARα agonists inhibit inflammatory activation of macrophages through upregulation of β-defensin 1

BACKGROUND

Effects of peroxisome proliferator-activated receptor alpha (PPARα) agonists on cardiovascular outcome have been controversial. Although these agents primarily affect lipoprotein metabolism, their pleiotropic anti-inflammatory effect is one of the potential anti-atherosclerotic mechanisms. This study aimed to evaluate the effect of fenofibrate and gemfibrozil on inflammation in macrophages and reveal pathways these agents may affect.

METHODS AND RESULTS

The two PPARα agonists inhibited secretion of CXCL2, TNF-α, IL-6, activation of p65 of NF-κB, ERK, and TLR4 expression. These changes occurred simultaneously with upregulation and secretion of β-defensin 1, an inflammation-modulating peptide. To demonstrate the role of β-defensin 1, it was knocked-down by target-specific siRNA. The effects of PPARα agonists on TLR4 expression and chemokine secretion were obviously abrogated with this treatment. In experiments investigating whether β-defensin 1 acts extracellularly, inflammatory chemokines decreased significantly after the addition of recombinant β-defensin 1 or conditioned media to cells. In experiments designed to clarify if the effects of the two agents are PPARα-dependent, induction of mRNA and secretion β-defensin 1 and inhibition of chemokine release were clearly reduced with GW6471, a PPARα blocker.

CONCLUSIONS

Our results reveal the pathways by which fenofibrate and gemfibrozil inhibit LPS-induced inflammatory activation of macrophages. This study elucidated a novel anti-inflammatory mechanism that acts through PPARα, β-defensin 1, and TLR4 pathways.

FAAH-mediated modulation of TLR3-induced neuroinflammation in the rat hippocampus

The present study examined the effect of enhancing fatty acid amide hydrolase (FAAH) substrate levels in vivo on Toll-like receptor (TLR)3-induced neuroinflammation. Systemic and central (i.c.v.) administration of the FAAH inhibitor URB597 increased hippocampal levels of the N-acylethanolamines palmitoylethanolamide and oleoylethanolamide, but not anandamide. Systemic URB597 increased IFNα, IFNγ and IL-6 expression following TLR3 activation and attenuated TLR3-induced IL-1β and TNFα expression. In comparison, central URB597 administration attenuated the TLR3-induced increase in TNFα and IFNγ expression (and associated downstream genes IP-10 and SOCS1), while concurrently increasing IL-10 expression. These data support an important role for FAAH-mediated regulation of TLR3-induced neuroinflammatory responses.

Exploring the complexity of pathway-drug relationships using latent Dirichlet allocation

Analysis of cellular responses to diverse stimuli enables the exploration in the complexity of functional genomics. Typically, high-throughput microarray data allow us to identify genes that are differentially expressed under a phenomenon of interest. To extract the meanings from the long list of those differentially expressed genes, we present a new method "pathway-based LDA" to determine pathways/gene sets that are perturbed after exposure to different chemicals. In this study, a pathway is defined as a group of functionally related genes. Specifically, we have implemented a probabilistic Latent Dirichlet Allocation (LDA) model to learn drug-pathway-gene relations by taking known gene-pathway memberships as prior knowledge. We applied the pathway-based LDA model and 236 known pathways in order to determine pathway responsiveness to gene expression data of 1169 drugs. Our method yielded a better predictive performance on pathway responsiveness to drug treatments than the existing methods. Moreover, the pathway-based LDA also revealed genes contributing the most in each pre-defined pathway through a probabilistic distribution of genes. In achieving that, our method could provide a useful estimator of the pathway complexity of a genome.

Nucleotide receptor P2RX7 stimulation enhances LPS-induced interferon-β production in murine macrophages

Stimulation of P2RX(7) with extracellular ATP potentiates numerous LPS-induced proinflammatory events, including cytokine induction in macrophages, but the molecular mechanisms underlying this process are not well defined. Although P2RX(7) ligation has been proposed to activate several transcription factors, many of the LPS-induced mediators affected by P2RX(7) activation are not induced by P2RX(7) agonists alone, suggesting a complementary role for P2RX(7) in transcriptional regulation. Type I IFN production, whose expression is tightly controlled by multiple transcription factors that form an enhanceosome, is critical for resistance against LPS-containing bacteria. The effect of purinergic receptor signaling on LPS-dependent type I IFN is unknown and would be of great relevance to a diverse array of inflammatory conditions. The present study demonstrates that stimulation of macrophages with P2RX(7) agonists substantially enhances LPS-induced IFN-β expression, and this enhancement is ablated in macrophages that do not express functional P2RX(7) or when the MAPK MEK1/2 pathways are inhibited. Potentiation of LPS-induced IFN-β expression following P2RX(7) stimulation is likely transcriptionally regulated, as this enhancement is observed at the IFN-β promoter level. Furthermore, P2RX(7) stimulation is able to increase the phosphorylation and subsequent IFN-β promoter occupancy of IRF-3, a transcription factor that is critical for IFN-β transcription by TLR agonists. This newly discovered role for P2RX(7) in IFN regulation may have implications in antimicrobial defense, which has been linked to P2RX(7) activation in other studies.

Lipids derived from virulent Francisella tularensis broadly inhibit pulmonary inflammation via toll-like receptor 2 and peroxisome proliferator-activated receptor α

Francisella tularensis is a Gram-negative facultative intracellular pathogen that causes an acute lethal respiratory disease in humans. The heightened virulence of the pathogen is linked to its unique ability to inhibit Toll-like receptor (TLR)-mediated inflammatory responses. The bacterial component and mechanism of this inhibition are unknown. Here we show that lipids isolated from virulent but not attenuated strains of F. tularensis are not detected by host cells, inhibit production of proinflammatory cytokines by primary macrophages in response to known TLR ligands, and suppress neutrophil recruitment in vivo. We further show that lipid-mediated inhibition of inflammation is dependent on TLR2, MyD88, and the nuclear hormone and fatty acid receptor peroxisome proliferator-activated receptor α (PPARα). Pathogen lipid-mediated interference with inflammatory responses through the engagement of TLR2 and PPARα represents a novel manipulation of host signaling pathways consistent with the ability of highly virulent F. tularensis to efficiently evade host immune responses.

Digital quantification of gene expression in sequential breast cancer biopsies reveals activation of an immune response

Advancements in molecular biology have unveiled multiple breast cancer promoting pathways and potential therapeutic targets. Large randomized clinical trials remain the ultimate means of validating therapeutic efficacy, but they require large cohorts of patients and are lengthy and costly. A useful approach is to conduct a window of opportunity study in which patients are exposed to a drug pre-surgically during the interval between the core needle biopsy and the definitive surgery. These are non-therapeutic studies and the end point is not clinical or pathological response but rather evaluation of molecular changes in the tumor specimens that can predict response. However, since the end points of the non-therapeutic studies are biologic, it is critical to first define the biologic changes that occur in the absence of treatment. In this study, we compared the molecular profiles of breast cancer tumors at the time of the diagnostic biopsy versus the definitive surgery in the absence of any intervention using the Nanostring nCounter platform. We found that while the majority of the transcripts did not vary between the two biopsies, there was evidence of activation of immune related genes in response to the first biopsy and further investigations of the immune changes after a biopsy in early breast cancer seem warranted.

Modulation of colonic inflammation in Mdr1a(-/-) mice by green tea polyphenols and their effects on the colon transcriptome and proteome

Animal models are an important tool to understand the complex pathogenesis of inflammatory bowel diseases (IBDs). This study tested the anti-inflammatory potential of a green tea extract rich in polyphenols (GrTP) in the colon of the multidrug resistance targeted mutation (Mdr1a(-/-)) mouse model of IBD. Insights into mechanisms responsible for this reduction in inflammation were gained using transcriptome and proteome analyses. Mice were randomly assigned to an AIN-76A (control) or GrTP-enriched diet. At 21 or 24 weeks of age, a colonic histological injury score was determined for each mouse, colon mRNA transcript levels were assessed using microarrays, and colon protein expression was measured using two-dimensional gel electrophoresis and liquid chromatography-mass spectrometry protein identification. Mean colonic histological injury score of GrTP-fed Mdr1a(-/-) mice was significantly lower compared to those fed the control diet. Microarray and proteomics analyses showed reduced abundance of transcripts and proteins associated with immune and inflammatory response and fibrinogenesis pathways, and increased abundance of those associated with xenobiotic metabolism pathways in response to GrTP, suggesting that its anti-inflammatory activity is mediated by multiple molecular pathways. Peroxisome proliferator-activated receptor-α and signal transducer and activator of transcription 1 appear to be two key molecules which regulate these effects. These results support the view that dietary intake of polyphenols derived from green tea can ameliorate intestinal inflammation in the colon of a mouse model of IBD, and are in agreement with studies suggesting that consumption of green tea may reduce IBD symptoms and therefore play a part in an overall IBD treatment regimen.

USP4 positively regulates RIG-I-mediated antiviral response through deubiquitination and stabilization of RIG-I

Protein ubiquitination plays an essential role in the regulation of retinoic acid-inducible gene I (RIG-I) activation and the antiviral immune response. However, the function of the opposite process of deubiquitination in RIG-I activation remains elusive. In this study, we have identified the deubiquitinating enzyme ubiquitin-specific protease 4 (USP4) as a new regulator for RIG-I activation through deubiquitination and stabilization of RIG-I. USP4 expression was attenuated after virus-induced RIG-I activation. Overexpression of USP4 significantly enhanced RIG-I protein expression and RIG-I-triggered beta interferon (IFN-β) signaling and, at the same time, inhibited vesicular stomatitis virus (VSV) replication. Small interfering RNA (siRNA) knockdown of USP4 expression had an opposite effect. Furthermore, USP4 was found to interact with RIG-I and remove K48-linked polyubiquitination chains from RIG-I. Therefore, we identified USP4 as a new positive regulator for RIG-I that acts through deubiquitinating K48-linked ubiquitin chains and stabilizing RIG-I.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Negative regulatory approaches to the attenuation of Toll-like receptor signaling

Toll-like receptors (TLRs) are pivotal components of the innate immune response, which is responsible for eradicating invading microorganisms through the induction of inflammatory molecules. These receptors are also involved in responding to harmful endogenous molecules and have crucial roles in the activation of the innate immune system and shaping the adaptive immune response. However, TLR signaling pathways must be tightly regulated because undue TLR stimulation may disrupt the fine balance between pro- and anti-inflammatory responses. Such disruptions may harm the host through the development of autoimmune and inflammatory diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Several studies have investigated the regulatory pathways of TLRs that are essential for modulating proinflammatory responses. These studies reported several pathways and molecules that act individually or in combination to regulate immune responses. In this review, we have summarized recent advancements in the elucidation of the negative regulation of TLR signaling. Moreover, this review covers the modulation of TLR signaling at multiple levels, including adaptor complex destabilization, phosphorylation and ubiquitin-mediated degradation of signal proteins, manipulation of other receptors, and transcriptional regulation. Lastly, synthetic inhibitors have also been briefly discussed to highlight negative regulatory approaches in the treatment of inflammatory diseases.

Ubiquitin-specific protease 4 promotes TNF-α-induced apoptosis by deubiquitination of RIP1 in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a common type of cancer. Better understanding of molecular aberrations associated with HNSCC might identify new diagnostic and therapeutic strategies for this disease. In this study, we found ubiquitin-specific protease 4 (USP4) was significantly upregulated in HNSCC. USP4 negatively regulates RIP1-mediated NF-κB activation and promotes TNF-α-induced apoptosis in FaDu cells. USP4 directly interacts with receptor-interacting protein 1 (RIP1) and deubiquitinates K63-linked ubiquitination from RIP1. Therefore, our results indicate that USP4 has tumor suppressor roles in HNSCC and suggest USP4 as a potential therapeutic target for HNSCC.

Activation and regulation of interferon-β in immune responses

Interferons (IFNs) were discovered more than half a century ago, and extensive research has since identified multifarious roles for type I IFN in human immune responses. Here, we review the functions of IFN-β in innate and adaptive immunity. We also discuss the activation and influence of IFN-β on myeloid cell types, including monocytes and dendritic cells, as well as address the effects of IFN-β on T cells and B cells. Findings from our own laboratory, which explores the molecular mechanisms of IFN-β activation by LPS and viruses, as well as from other groups investigating the regulation of IFN-β by viral proteins and endogenous factors are described. The effects of post-translational modifications of the interferon regulatory factor (IRF)-3 on IFN-β induction are also highlighted. Many unanswered questions remain concerning the regulation of the type I IFN response in inflammation, especially the role of transcription factors in the modulation of inflammatory gene expression, and these questions will form the basis for exciting avenues of future research.

TRAF-interacting protein (TRIP) negatively regulates IFN-β production and antiviral response by promoting proteasomal degradation of TANK-binding kinase 1

TRAF-interacting protein (TRIP) negatively regulates TLR3/4- and RIG-I–induced IFN-β signaling by promoting K48-linked ubiquitination and proteasomal degradation of TBK1.

TANK-binding kinase 1 (TBK1) plays an essential role in Toll-like receptor (TLR)– and retinoic acid–inducible gene I (RIG-I)–mediated induction of type I interferon (IFN; IFN-α/β) and host antiviral responses. How TBK1 activity is negatively regulated remains largely unknown. We report that TNF receptor-associated factor (TRAF)–interacting protein (TRIP) promotes proteasomal degradation of TBK1 and inhibits TLR3/4- and RIG-I–induced IFN-β signaling. TRIP knockdown resulted in augmented activation of IFN regulatory factor 3 (IRF3) and enhanced expression of IFN-β in TLR3/4- and RIG-I–activated primary peritoneal macrophages, whereas overexpression of TRIP had opposite effects. Consistently, TRIP impaired Sendai virus (SeV) infection–induced IRF3 activation and IFN-β production and promoted vesicular stomatitis virus (VSV) replication. As an E3 ubiquitin ligase, TRIP negatively regulated the cellular levels of TBK1 by directly binding to and promoting K48-linked polyubiquitination of TBK1. Therefore, we identified TRIP as a negative regulator in TLR3/4- and RIG-I–triggered antiviral responses and suggested TRIP as a potential target for the intervention of diseases with uncontrolled IFN-β production.

Peptidoglycan induced expression of peroxisome proliferator-activated receptor γ in mouse peritoneal macrophages: role of ERK and JNK MAP kinases

The peroxisome proliferator-activated receptor (PPAR) γ plays an important role in macrophage inflammatory homeostasis. Here we investigate the cross talk between PPARγ and TLR2 signaling pathway in mouse peritoneal macrophages. Real time RT-PCR and immunoblot analysis revealed that peptidoglycan (PGN) treatment of macrophages leads to biphasic effect on PPARγ expression i.e. an early upregulation and a late suppression. Inhibition of ERK MAP kinase by PD98059 abolished the early and rapid induction of PPARγ, while the inhibition of JNK MAP kinase by SP600125 nullifies the late inhibitory effect on the PPARγ expression in a dose-dependent manner. Furthermore, PPARγ knockdown macrophages showed enhanced NF-κB activity after PGN treatment. PGN treatment also enhances PPARγ interaction with p65 as observed by immunoprecipitation. This interaction may inhibit NF-κB (p65) activity as increased nuclear localization of p65 was observed in PPARγ knockdown macrophages after PGN treatment. PPARγ knockdown also increased the PGN-induced inflammatory cytokines (TNF-α, IL-1β, IL-12p40) production. Thus, our observations suggest that PGN induces PPARγ expression which is regulated by MAPKs activation and this enhanced PPARγ in turn attenuate NF-κB activity probably via enhancing p65 nuclear export. These results provide insight into how these pathways could be modulated in inflammatory diseases.

PPARs at the crossroads of lipid signaling and inflammation

Nuclear receptors (NRs) are ligand-dependent transcription factors whose activation affects genes controlling vital processes. Among them, the peroxisome proliferator-activated receptors (PPARs) have emerged as links between lipids, metabolic diseases, and innate immunity. PPARs are activated by fatty acids and their derivatives, many of which also signal through membrane receptors, thereby creating a lipid signaling network between the cell surface and the nucleus. Tissues that play a role in whole-body metabolic homeostasis, such as adipose tissue, liver, skeletal muscle, intestines, and blood vessel walls, are prone to inflammation when metabolism is disturbed, a complication that promotes type 2 diabetes and cardiovascular disease. This review discusses the protective roles of PPARs in inflammatory conditions and the therapeutic anti-inflammatory potential of PPAR ligands.

Network analysis identifies a putative role for the PPAR and type 1 interferon pathways in glucocorticoid actions in asthmatics

BACKGROUND

Asthma is a chronic inflammatory airway disease influenced by genetic and environmental factors that affects ~300 million people worldwide, leading to ~250,000 deaths annually. Glucocorticoids (GCs) are well-known therapeutics that are used extensively to suppress airway inflammation in asthmatics. The airway epithelium plays an important role in the initiation and modulation of the inflammatory response. While the role of GCs in disease management is well understood, few studies have examined the holistic effects on the airway epithelium.

METHODS

Gene expression data were used to generate a co-transcriptional network, which was interrogated to identify modules of functionally related genes. In parallel, expression data were mapped to the human protein-protein interaction (PPI) network in order to identify modules with differentially expressed genes. A common pathways approach was applied to highlight genes and pathways functionally relevant and significantly altered following GC treatment.

RESULTS

Co-transcriptional network analysis identified pathways involved in inflammatory processes in the epithelium of asthmatics, including the Toll-like receptor (TLR) and PPAR signaling pathways. Analysis of the PPI network identified RXRA, PPARGC1A, STAT1 and IRF9, among others genes, as differentially expressed. Common pathways analysis highlighted TLR and PPAR signaling pathways, providing a link between general inflammatory processes and the actions of GCs. Promoter analysis identified genes regulated by the glucocorticoid receptor (GCR) and PPAR pathways as well as highlighted the interferon pathway as a target of GCs.

CONCLUSIONS

Network analyses identified known genes and pathways associated with inflammatory processes in the airway epithelium of asthmatics. This workflow illustrated a hypothesis generating experimental design that integrated multiple analysis methods to produce a weight-of-evidence based approach upon which future focused studies can be designed. In this case, results suggested a mechanism whereby GCs repress TLR-mediated interferon production via upregulation of the PPAR signaling pathway. These results highlight the role of interferons in asthma and their potential as targets of future therapeutic efforts.

Tripartite motif-containing protein 38 negatively regulates TLR3/4- and RIG-I-mediated IFN-β production and antiviral response by targeting NAP1

Recognition of RNA virus through TLR and RIG-I-like receptor results in rapid expression of type I IFNs, which play an essential role in host antiviral responses. However, the mechanisms to terminate the production of type I IFNs are not well defined. In the current study, we identified a member of the tripartite motif (TRIM) family, TRIM38, as a negative regulator in TLR3/4- and RIG-I-mediated IFN-β signaling. Knockdown of TRIM38 expression by small interfering RNA resulted in augmented activation of IFN regulatory factor 3 and enhanced expression of IFN-β, whereas overexpression of TRIM38 had opposite effects. Coimmunoprecipitation and colocalization experiments demonstrated that TRIM38 interacted with NF-κB-activating kinase-associated protein 1 (NAP1), which is required for TLR-induced IFN regulatory factor 3 activation and IFN-β production. As an E3 ligase, TRIM38 promoted K48-linked polyubiquitination and proteasomal degradation of NAP1. Thus, knockdown of TRIM38 expression resulted in higher protein level of NAP1 in primary macrophages. Consistent with the inhibitory roles in TLR3/4- and RIG-I-mediated IFN-β signaling, knockdown of TRIM38 significantly inhibited the replication of vesicular stomatitis virus. Overexpression of TRIM38 resulted in enhanced replication of vesicular stomatitis virus. Therefore, our results demonstrate that TRIM38 is a negative regulator for TLR and RIG-I-mediated IFN-β production by targeting NAP1 for ubiquitination and subsequent proteasome-mediated degradation.

TLR-induced NF-κB activation regulates NLRP3 expression in murine macrophages

NLRP3 inflammasome plays a critical role in the activation of caspase-1 and maturation of IL-1β. However, the specific cis- and trans-regulatory elements that determine the extent of NLRP3 expression are not well defined. In this study, we found NLRP3 expression was induced by TLR agonists in murine macrophages in a NF-κB dependent manner. Furthermore, the corresponding NF-κB binding sites (nt -1303 to -1292 and -1238 to -1228) were identified in the NLRP3 promoter. Finally, EMSA and ChIP assays demonstrated LPS-induced NF-κB binding to the NLRP3 promoter. Therefore, out results delineated the molecular mechanisms involved in TLR-induced transcriptional regulation of NLRP3.

LY294002 inhibits TLR3/4-mediated IFN-β production via inhibition of IRF3 activation with a PI3K-independent mechanism

TLR3 and TLR4 utilize adaptor TRIF to activate interferon regulatory factor 3 (IRF3), resulting in interferon β (IFN-β) production to mediate anti-viral infection. In this report, we analyzed the effect of two known phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 and wortmannin on LPS- and poly(I:C)-induced IFN-β production in peritoneal macrophages. LY294002 inhibited LPS- and poly(I:C)-induced IFN-β transcription and secretion. In contrast, wortmannin could not inhibit IFN-β production. Furthermore, IRF3 transcriptional activation and binding to IFN-β promoter were found to be inhibited by LY294002. Therefore, our findings demonstrate LY294002 negatively regulates LPS- and poly(I:C)-induced IFN-β production through inhibition of IRF3 activation in a PI3K-independent manner.