Targeting mRNA stability arrests inflammatory bone loss

Prediction of Interactomic HUB Genes in Periodontitis With Acute Myocardial Infarction

BACKGROUND

Acute myocardial infarction (AMI) risk correlates with C-reactive protein (CRP) levels, suggesting systemic inflammation is present well before AMI. Studying different types of periodontal disease (PD), extremely common in individuals at risk for AMI, has been one important research topic. According to recent research, AMI and PD interact via the systemic production of certain proinflammatory and anti-inflammatory cytokines, small signal molecules, and enzymes that control the onset and development of both disorders' chronic inflammatory reactions. This study uses machine learning to identify the interactome hub biomarker genes in acute myocardial infarction and periodontitis.

METHODS

GSE208194 and GSE222883 were chosen for our research after a thorough search using keywords related to the study's goal from the gene expression omnibus (GEO) datasets. DEGs were identified from the GEOR tool, and the hub gene was identified using Cytoscape-cytohubba. Using expression values, Random Forest, Adaptive Boosting, and Naive Bayes, widgets-generated transcriptomics data, were labelled, and divided into 80/20 training and testing data with cross-validation. ROC curve, confusion matrix, and AUC were determined. In addition, Functional Enrichment Analysis of Differentially Expressed Gene analysis was performed.

RESULTS

Random Forest, AdaBoost, and Naive Bayes models with 99%, 100%, and 75% AUC, respectively. Compared to RF, AdaBoost, and NB classification models, AdaBoost had the highest AUC. Categorization algorithms may be better predictors than important biomarkers.

CONCLUSIONS

Machine learning model predicts hub and non-hub genes from genomic datasets with periodontitis and acute myocardial infarction.

Tristetraprolin regulates the skeletal phenotype and osteoclastogenic potential through monocytic myeloid-derived suppressor cells

Tristetraprolin (TTP; also known as NUP475, GOS24, or TIS11), encoded by Zfp36, is an RNA-binding protein that regulates target gene expression by promoting mRNA decay and preventing translation. Although previous studies have indicated that TTP deficiency is associated with systemic inflammation and a catabolic-like skeletal phenotype, the mechanistic underpinnings remain unclear. Here, using both TTP-deficient (TTPKO) and myeloid-specific TTPKO (cTTPKO) mice, we reveal that global absence or loss of TTP in the myeloid compartment results in a reduced bone microarchitecture, whereas gain-of-function TTP knock-in (TTPKI) mice exhibit no significant loss of bone microarchitecture. Flow cytometry analysis revealed a significant immunosuppressive immune cell phenotype with increased monocytic myeloid-derived suppressor cells (M-MDSCs) in TTPKO and cTTPKO mice, whereas no significant changes were observed in TTPKI mice. Single-cell transcriptomic analyses of bone marrow myeloid progenitor cell populations indicated a dramatic increase in early MDSC marker genes for both cTTPKO and TTPKO bone marrow populations. Consistent with these phenotypic and transcriptomic data, in vitro osteoclastogenesis analysis of bone marrow M-MDSCs from cTTPKO and TTPKO displayed enhanced osteoclast differentiation and functional capacity. Focused transcriptomic analyses of differentiated M-MDSCs showed increased osteoclast-specific transcription factors and cell fusion gene expression. Finally, functional data showed that M-MDSCs from TTP loss-of-function mice were capable of osteoclastogenesis and bone resorption in a context-dependent manner. Collectively, these findings indicate that TTP plays a central role in regulating osteoclastogenesis through multiple mechanisms, including induction of M-MDSCs that appear to regulate skeletal phenotype.

RNA-Binding Proteins as a Molecular Link between COPD and Lung Cancer

Chronic obstructive pulmonary disease (COPD) represents an independent risk factor for lung cancer development. Accelerated cell senescence, induced by oxidative stress and inflammation, is a common pathogenic determinant of both COPD and lung cancer. The post transcriptional regulation of genes involved in these processes is finely regulated by RNA-binding proteins (RBPs), which regulate mRNA turnover, subcellular localization, splicing and translation. Multiple pro-inflammatory mediators (including cytokines, chemokines, proteins, growth factors and others), responsible of lung microenvironment alteration, are regulated by RBPs. Several mouse models have shown the implication of RBPs in multiple mechanisms that sustain chronic inflammation and neoplastic transformation. However, further studies are required to clarify the role of RBPs in the pathogenic mechanisms shared by lung cancer and COPD, in order to identify novel biomarkers and therapeutic targets. This review will therefore focus on the studies collectively indicating the role of RBPs in oxidative stress and chronic inflammation as common pathogenic mechanisms shared by lung cancer and COPD.

The nexus between RNA-binding proteins and their effectors

RNA-binding proteins (RBPs) regulate essentially every event in the lifetime of an RNA molecule, from its production to its destruction. Whereas much has been learned about RNA sequence specificity and general functions of individual RBPs, the ways in which numerous RBPs instruct a much smaller number of effector molecules, that is, the core engines of RNA processing, as to where, when and how to act remain largely speculative. Here, we survey the known modes of communication between RBPs and their effectors with a particular focus on converging RBP-effector interactions and their roles in reducing the complexity of RNA networks. We discern the emerging unifying principles and discuss their utility in our understanding of RBP function, regulation of biological processes and contribution to human disease.

Intestinal Flora-Derived Kynurenic Acid Protects Against Intestinal Damage Caused by Candida albicans Infection via Activation of Aryl Hydrocarbon Receptor

Colonization of the intestinal tract by Candida albicans (C. albicans) can lead to invasive candidiasis. Therefore, a functional intestinal epithelial barrier is critical for protecting against invasive C. albicans infections. We collected fecal samples from patients with Candida albicans bloodstream infection and healthy people. Through intestinal flora 16sRNA sequencing and intestinal metabolomic analysis, we found that C. albicans infection resulted in a significant decrease in the expression of the metabolite kynurenic acid (KynA). We used a repeated C. albicans intestinal infection mouse model, established following intake of 3% dextran sulfate sodium salt (DSS) for 9 days, and found that KynA, a tryptophan metabolite, inhibited inflammation, promoted expression of intestinal tight junction proteins, and protected from intestinal barrier damage caused by invasive Candida infections. We also demonstrated that KynA activated aryl hydrocarbon receptor (AHR) repressor in vivo and in vitro. Using Caco-2 cells co-cultured with C. albicans, we showed that KynA activated AHR, inhibited the myosin light chain kinase-phospho-myosin light chain (MLCK-pMLC) signaling pathway, and promoted tristetraprolin (TTP) expression to alleviate intestinal inflammation. Our findings suggest that the metabolite KynA which is differently expressed in patients with C. albicans infection and has a protective effect on the intestinal epithelium, via activating AHR, could be explored to provide new potential therapeutic strategies for invasive C. albicans infections.

Post-Transcriptional Regulation of Immune Responses and Inflammatory Diseases by RNA-Binding ZFP36 Family Proteins

Post-transcriptional regulation is involved in the regulation of many inflammatory genes. Zinc finger protein 36 (ZFP36) family proteins are RNA-binding proteins involved in messenger RNA (mRNA) metabolism pathways. The ZFP36 family is composed of ZFP36 (also known as tristetraprolin, TTP), ZFP36L1, ZFP36L2, and ZFP36L3 (only in rodents). The ZFP36 family proteins contain two tandemly repeated CCCH-type zinc-finger motifs, bind to adenine uridine-rich elements in the 3’-untranslated regions (3’ UTR) of specific mRNA, and lead to target mRNA decay. Although the ZFP36 family members are structurally similar, they are known to play distinct functions and regulate different target mRNAs, probably due to their cell-type-specific expression patterns. For instance, ZFP36 has been well-known to function as an anti-inflammatory modulator in murine models of systemic inflammatory diseases by down-regulating the production of various pro-inflammatory cytokines, including TNF-α. Meanwhile, ZFP36L1 is required for the maintenance of the marginal-zone B cell compartment. Recently, we found that ZFP36L2 reduces the expression of Ikzf2 (encoding HELIOS) and suppresses regulatory T cell function. This review summarizes the current understanding of the post-transcriptional regulation of immunological responses and inflammatory diseases by RNA-binding ZFP36 family proteins.

RBPs Play Important Roles in Vascular Endothelial Dysfunction Under Diabetic Conditions

Diabetes is one of the major health care problems worldwide leading to huge suffering and burden to patients and society. Diabetes is also considered as a cardiovascular disorder because of the correlation between diabetes and an increased incidence of cardiovascular disease. Vascular endothelial cell dysfunction is a major mediator of diabetic vascular complications. It has been established that diabetes contributes to significant alteration of the gene expression profile of vascular endothelial cells. Post-transcriptional regulation by RNA binding proteins (RBPs) plays an important role in the alteration of gene expression profile under diabetic conditions. The review focuses on the roles and mechanisms of critical RBPs toward diabetic vascular endothelial dysfunction. Deeper understanding of the post- transcriptional regulation by RBPs could lead to new therapeutic strategies against diabetic manifestation in the future.

Silk Fibroin-Alginate-Hydroxyapatite Composite Particles in Bone Tissue Engineering Applications In Vivo

The aim of this study was to evaluate the in vivo bone regeneration capability of alginate (AL), AL/hydroxyapatite (HA), and AL/HA/silk fibroin (SF) composites. Forty Sprague Dawley rats were used for the animal experiments. Central calvarial bone (diameter: 8.0 mm) defects were grafted with AL, AL/HA, or AL/HA/SF. New bone formation was evaluated by histomorphometric analysis. To demonstrate the immunocompatibility of each group, the level of tumor necrosis factor (TNF)-α expression was studied by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (qRT-PCR) at eight weeks post implantation. Additionally, osteogenic markers, such as fibroblast growth factor (FGF)-23, osteoprotegerin (OPG), and Runt-related transcription factor (Runx2) were evaluated by qPCR or IHC at eight weeks post implantation. The AL/HA/SF group showed significantly higher new bone formation than did the control group (p = 0.044) and the AL group (p = 0.035) at four weeks post implantation. Additionally, the AL/HA/SF group showed lower relative TNF-α mRNA levels and higher FGF-23 mRNA levels than the other groups did at eight weeks post implantation. IHC results demonstrated that the AL/HA/SF group had lower TNF-α expression and higher OPG and Runx2 expression at eight weeks post implantation. Additionally, no evidence of the inflammatory reaction or giant cell formation was observed around the residual graft material. We concluded that the AL/HA/SF composite could be effective as a scaffold for bone tissue engineering.

Tristetraprolin as a Therapeutic Target in Inflammatory Disease

Members of the tristetraprolin (TTP) family of RNA-binding proteins are found in all major eukaryotic groups. TTP family members, from plants through humans, can bind adenosine-uridine rich elements in target mRNAs with high affinity. In mammalian cells, these proteins then promote deadenylation and decay of target transcripts. Four such proteins are found in mice, of which the best studied is TTP. When the gene encoding TTP is disrupted in mice, the animals develop a severe syndrome of arthritis, autoimmunity, cachexia, dermatitis, and myeloid hyperplasia. Conversely, recent overexpression studies have demonstrated protection against several experimental models of immune inflammatory disease. This endogenous anti-inflammatory protein could serve as the basis for novel approaches to therapy of similar conditions in humans.

Enhanced stability of tristetraprolin mRNA protects mice against immune-mediated inflammatory pathologies

Tristetraprolin (TTP) is an inducible, tandem zinc-finger mRNA binding protein that binds to adenylate-uridylate-rich elements (AREs) in the 3'-untranslated regions (3'UTRs) of specific mRNAs, such as that encoding TNF, and increases their rates of deadenylation and turnover. Stabilization of Tnf mRNA and other cytokine transcripts in TTP-deficient mice results in the development of a profound, chronic inflammatory syndrome characterized by polyarticular arthritis, dermatitis, myeloid hyperplasia, and autoimmunity. To address the hypothesis that increasing endogenous levels of TTP in an intact animal might be beneficial in the treatment of inflammatory diseases, we generated a mouse model (TTPΔARE) in which a 136-base instability motif in the 3'UTR of TTP mRNA was deleted in the endogenous genetic locus. These mice appeared normal, but cultured fibroblasts and macrophages derived from them exhibited increased stability of the otherwise highly labile TTP mRNA. This resulted in increased TTP protein expression in LPS-stimulated macrophages and increased levels of TTP protein in mouse tissues. TTPΔARE mice were protected from collagen antibody-induced arthritis, exhibited significantly reduced inflammation in imiquimod-induced dermatitis, and were resistant to induction of experimental autoimmune encephalomyelitis, presumably by dampening the excessive production of proinflammatory mediators in all cases. These data suggest that increased systemic levels of TTP, secondary to increased stability of its mRNA throughout the body, can be protective against inflammatory disease in certain models and might be viewed as an attractive therapeutic target for the treatment of human inflammatory diseases.

Cell- and Gene- Based Therapeutics for Periodontal Regeneration

Periodontitis is a disease of the periodontium, characterized by loss of connective tissue attachment and supporting the alveolar bone. Therefore, to regenerate these lost tissues of the periodontium researchers have included a variety of surgical procedures including grafting materials growth factors and the use of barrier membranes, ultimately resulting into regeneration that is biologically possible but clinically unpredictable. Recently a newer approach of delivering DNA plasmids as therapeutic agents is gaining special attention and is called gene delivery method. Gene therapy being considered a novel approach have a potential to channel their signals in a very systematic and controlled manner thereby providing encoded proteins at all stages of tissue regeneration. The aim of this review was to enlighten a view on the application involving gene delivery and tissue engineering in periodontal regeneration.

Aggregatibacter actinomycetemcomitans, a potent immunoregulator of the periodontal host defense system and alveolar bone homeostasis

Aggregatibacter actinomycetemcomitans is a perio-pathogenic bacteria that has long been associated with localized aggressive periodontitis. The mechanisms of its pathogenicity have been studied in humans and preclinical experimental models. Although different serotypes of A. actinomycetemcomitans have differential virulence factor expression, A. actinomycetemcomitans cytolethal distending toxin (CDT), leukotoxin, and lipopolysaccharide (LPS) have been most extensively studied in the context of modulating the host immune response. Following colonization and attachment in the oral cavity, A. actinomycetemcomitans employs CDT, leukotoxin, and LPS to evade host innate defense mechanisms and drive a pathophysiologic inflammatory response. This supra-physiologic immune response state perturbs normal periodontal tissue remodeling/turnover and ultimately has catabolic effects on periodontal tissue homeostasis. In this review, we have divided the host response into two systems: non-hematopoietic and hematopoietic. Non-hematopoietic barriers include epithelium and fibroblasts that initiate the innate immune host response. The hematopoietic system contains lymphoid and myeloid-derived cell lineages that are responsible for expanding the immune response and driving the pathophysiologic inflammatory state in the local periodontal microenvironment. Effector systems and signaling transduction pathways activated and utilized in response to A. actinomycetemcomitans will be discussed to further delineate immune cell mechanisms during A. actinomycetemcomitans infection. Finally, we will discuss the osteo-immunomodulatory effects induced by A. actinomycetemcomitans and dissect the catabolic disruption of balanced osteoclast-osteoblast-mediated bone remodeling, which subsequently leads to net alveolar bone loss.

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.

Post-transcriptional control of cytokine gene expression in health and disease

Post-transcriptional control of cytokine gene expression is essential for rapid and transient response to stimuli and external stress. In health, post-transcriptional control is exerted by a number of trans-acting RNA-binding proteins and cis-acting sequence elements. These elements exist largely in the 3' untranslated region and comprise microRNA targets and notably AU-rich elements, and exert regulated mRNA decay and translation repression. Defects in this control can lead to increased and sustained production of pro-inflammatory mediators contributing to several chronic inflammatory disease and cancer states. This introduction to the Journal's special issue on the topic summarizes, in a non-comprehensive list, the types of RNA-binding protein and their target cytokines, and potential contributions to disease, and presents the highlights of the individual reviews.

Luteolin inhibits inflammatory responses via p38/MK2/TTP-mediated mRNA stability

Luteolin (Lut) is a common dietary flavonoid present in Chinese herbal medicines that has been reported to have important anti-inflammatory properties. The purposes of this study were to observe the inhibition of lipopolysaccharide (LPS)-induced inflammatory responses in bone marrow macrophages (BMM) by Lut, and to examine whether this inhibition involves p38/MK2/TTP-mediated mRNA stability. Lut suppressed the production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in a dose-dependent manner according to enzyme-linked immunosorbent assay (ELISA) analysis. Lut also shortened the half-lives of the TNF-α and IL-6 mRNAs according to real-time PCR analysis. Western blots were performed to assess the activation of p38 and MK2 as well as the expression of TTP. The results indicated that Lut inhibited p38 and MK2 phosphorylation while promoting TTP expression. These results suggest that the anti-inflammatory effects of Lut are partially mediated through p38/MK2/TTP-regulated mRNA stability.

Multiple functions of tristetraprolin/TIS11 RNA-binding proteins in the regulation of mRNA biogenesis and degradation

Members of the tristetraprolin (TTP/TIS11) family are important RNA-binding proteins initially characterized as mediators of mRNA degradation. They act via their interaction with AU-rich elements present in the 3'UTR of regulated transcripts. However, it is progressively appearing that the different steps of mRNA processing and fate including transcription, splicing, polyadenylation, translation, and degradation are coordinately regulated by multifunctional integrator proteins that possess a larger panel of functions than originally anticipated. Tristetraprolin and related proteins are very good examples of such integrators. This review gathers the present knowledge on the functions of this family of RNA-binding proteins, including their role in AU-rich element-mediated mRNA decay and focuses on recent advances that support the concept of their broader involvement in distinct steps of mRNA biogenesis and degradation.

Tristetraprolin (TTP): interactions with mRNA and proteins, and current thoughts on mechanisms of action

Changes in mRNA stability and translation are critical control points in the regulation of gene expression, particularly genes encoding growth factors, inflammatory mediators, and proto-oncogenes. Adenosine and uridine (AU)-rich elements (ARE), often located in the 3' untranslated regions (3'UTR) of mRNAs, are known to target transcripts for rapid decay. They are also involved in the regulation of mRNA stability and translation in response to extracellular cues. This review focuses on one of the best characterized ARE binding proteins, tristetraprolin (TTP), the founding member of a small family of CCCH tandem zinc finger proteins. In this survey, we have reviewed the current status of TTP interactions with mRNA and proteins, and discussed current thinking about TTP's mechanism of action to promote mRNA decay. We also review the proposed regulation of TTP's functions by phosphorylation. Finally, we have discussed emerging evidence for TTP operating as a translational regulator. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Genetic polymorphisms in RNA binding proteins contribute to breast cancer survival

The RNA-binding proteins TTP and HuR control expression of numerous genes associated with breast cancer pathogenesis by regulating mRNA stability. However, the role of genetic variation in TTP (ZFP36) and HuR (ELAVL1) genes is unknown in breast cancer prognosis. A total of 251 breast cancer patients (170 Caucasians and 81 African-Americans) were enrolled and followed up from 2001 to 2011 (or until death). Genotyping was performed for 10 SNPs in ZFP36 and 7 in ELAVL1 genes. On comparing both races with one another, significant differences were found for clinical and genetic variables. The influence of genetic polymorphisms on survival was analyzed by using Cox-regression, Kaplan-Meier analysis and the log-rank test. Univariate (Kaplan-Meier/Cox-regression) and multivariate (Cox-regression) analysis showed that the TTP gene polymorphism ZFP36*2 A > G was significantly associated with poor prognosis of Caucasian patients (HR = 2.03; 95% CI = 1.09-3.76; p = 0.025; log-rank p = 0.022). None of the haplotypes, but presence of more than six risk genotypes in Caucasian patients, was significantly associated with poor prognosis (HR=2.42; 95% CI = 1.17-4.99; p = 0.017; log-rank p = 0.007). The effect of ZFP36*2 A > G on gene expression was evaluated from patients' tissue samples. Both TTP mRNA and protein expression was significantly decreased in ZFP36*2 G allele carriers compared to A allele homozygotes. Conversely, upregulation of the TTP-target gene COX-2 was observed ZFP36*2 G allele carriers. Through its ability to attenuate TTP gene expression, the ZFP36*2 A > G gene polymorphism has appeared as a novel prognostic breast cancer marker in Caucasian patients.

MKP-1 is essential for canonical vitamin D-induced signaling through nuclear import and regulates RANKL expression and function

Vitamin D(3,) and its most active form, 1,25(OH)(2)D(3), are well known to stimulate osteoclastogenesis through stromal cell induction of the receptor activator of nuclear factor-κB ligand (RANKL). MAPK phosphatase-1 (MKP-1) is a phosphatase classically known to negatively regulate the innate immune response through dephosphorylation of p38, ERK, and c-Jun N-terminal kinase activity. This paper describes a new function of MKP-1 in permitting genomic 1,25(OH)(2)D(3) signaling and downstream osteoclastogenesis through RANKL. Initially, quantitative RT-PCR (qRT-PCR) and immunoblot analysis comparing bone marrow stromal cells (BMSC) revealed that 1,25(OH)(2)D(3)-induced vitamin D receptor (VDR), cytochrome P 45024a1, and RANKL mRNA expression and protein were significantly attenuated or absent in MKP-1(-/-) BMSC. Immunoblot analysis from cellular fractions of wild type and MKP-1(-/-) BMSC stimulated with 10(-7) m 1,25(OH)(2)D(3) revealed retinoid X receptor (RXR)α nuclear import was impaired in MKP-1(-/-) BMSC, whereas VDR import was not. Proximity ligation assays revealed that baseline VDR-RXRα heterodimer translocation was unchanged, yet 1,25(OH)(2)D(3)-induced nuclear translocation of VDR-RXRα heterodimers was reduced in MKP-1(-/-) BMSC. A functional consequence was observed as BMSC from MKP-1(-/-) mice treated with 1,25(OH)(2)D(3) and cocultured with RAW 264.7 cells had a 91% decrease in osteoclastogenesis and a 94.5% decrease in mineralized matrix resorption compared with wild-type cocultures (P < 0.01). These results reveal an unexpected, permissive role for MKP-1 in canonical 1,25(OH)(2)D(3) signaling via VDR-RXRα heterodimer nuclear import and downstream osteoclastogenesis through stromal cell RANKL expression.

3,6'-Dithiothalidomide, a new TNF-α synthesis inhibitor, attenuates the effect of Aβ1-42 intracerebroventricular injection on hippocampal neurogenesis and memory deficit

Evidence indicates altered neurogenesis in neurodegenerative diseases associated with inflammation, including Alzheimer's disease (AD). Neuroinflammation and its propagation have a critical role in the degeneration of hippocampal neurons, cognitive impairment, and altered neurogenesis. Particularly, tumor necrosis factor (TNF)-α plays a central role in initiating and regulating the cytokine cascade during an inflammatory response and is up-regulated in brain of AD patients. In this study, we investigated the effects of a novel thalidomide-based TNF-α lowering drug, 3,6'-dithiothalidomide, on hippocampal progenitor cell proliferation, neurogenesis and, memory tasks after intracerebroventricular injection of β-amyloid (Aß)(1-42) peptide. Seven days after Aβ(1-42) injection, a significant proliferation of hippocampal progenitor cells and memory impairment were evident. Four weeks after Aβ(1-42) peptide injection, elevated numbers of surviving 5-bromo-2'-deoxyuridine cells and newly formed neurons were detected. Treatment with 3,6'-dithiothalidomide attenuated these Aβ(1-42) provoked effects. Our data indicate that although treatment with 3,6'-dithiothalidomide in part attenuated the increase in hippocampal neurogenesis caused by Aβ(1-42) -induced neuroinflammation, the drug prevented memory deficits associated with increased numbers of activated microglial cells and inflammatory response. Therefore, 3,6'-dithiothalidomide treatment likely reduced neuronal tissue damage induced by neuroinflammation following Aβ(1-42) injection. Understanding the modulation of neurogenesis, and its relationship with memory function could open new therapeutic interventions for AD and other neurodegenerative disorders with an inflammatory component.

Tumor necrosis factor-α synthesis inhibitor 3,6'-dithiothalidomide attenuates markers of inflammation, Alzheimer pathology and behavioral deficits in animal models of neuroinflammation and Alzheimer's disease

BACKGROUND

Neuroinflammation is associated with virtually all major neurodegenerative disorders, including Alzheimer's disease (AD). Although it remains unclear whether neuroinflammation is the driving force behind these disorders, compelling evidence implicates its role in exacerbating disease progression, with a key player being the potent proinflammatory cytokine TNF-α. Elevated TNF-α levels are commonly detected in the clinic and animal models of AD.

METHODS

The potential benefits of a novel TNF-α-lowering agent, 3,6'-dithiothalidomide, were investigated in cellular and rodent models of neuroinflammation with a specific focus on AD. These included central and systemic inflammation induced by lipopolysaccharide (LPS) and Aβ(1-42) challenge, and biochemical and behavioral assessment of 3xTg-AD mice following chronic 3,6'-dithiothaliodmide.

RESULTS

3,6'-Dithiothaliodmide lowered TNF-α, nitrite (an indicator of oxidative damage) and secreted amyloid precursor protein (sAPP) levels in LPS-activated macrophage-like cells (RAW 264.7 cells). This translated into reduced central and systemic TNF-α production in acute LPS-challenged rats, and to a reduction of neuroinflammatory markers and restoration of neuronal plasticity following chronic central challenge of LPS. In mice centrally challenged with A(β1-42) peptide, prior systemic 3,6'-dithiothalidomide suppressed Aβ-induced memory dysfunction, microglial activation and neuronal degeneration. Chronic 3,6'-dithiothalidomide administration to an elderly symptomatic cohort of 3xTg-AD mice reduced multiple hallmark features of AD, including phosphorylated tau protein, APP, Aβ peptide and Aβ-plaque number along with deficits in memory function to levels present in younger adult cognitively unimpaired 3xTg-AD mice. Levels of the synaptic proteins, SNAP25 and synaptophysin, were found to be elevated in older symptomatic drug-treated 3xTg-AD mice compared to vehicle-treated ones, indicative of a preservation of synaptic function during drug treatment.

CONCLUSIONS

Our data suggest a strong beneficial effect of 3,6'-dithiothalidomide in the setting of neuroinflammation and AD, supporting a role for neuroinflammation and TNF-α in disease progression and their targeting as a means of clinical management.

Posttranscriptional Gene Regulation: Novel Pathways for Glucocorticoids' Anti-inflammatory Action

Posttranscriptional gene regulation (PTR) is a fundamental biological process that integrates with the master transcriptional control of gene expression, in ways that only in the last decade have been increasingly understood [1, 2]. While epigenetic and transcriptional events shape cell response qualitatively, deciding the pattern of gene expression to 'switch on or off' in response to endogenous or environmental triggers, the key task of PTR is to act as a 'rheostat' and rapidly adapt the cellular response by providing the appropriate amplitude and timing to the protein expression patterns [3, 4]. The pivotal role of this mechanism comes to the forefront in inflammatory and immune response, where the changes in amplitude and duration in the expression of dangerous and protective genes are in delicate balance, and are critical in determining either the successful resolution of the immune response or its chronic overexpression [5]. This brief review introduces members of the main classes of molecules mediating the cytoplasmic arm of gene regulation, namely RNA-binding proteins and micro-RNA (miRNA), and summarizes experimental data that underscore the role of these molecules in the pathophysiology of chronic inflammation, as well as their promising value as mechanisms conveying the anti-inflammatory effect of synthetic glucocorticoids.

The roles of TTP and BRF proteins in regulated mRNA decay

Adenylate- and uridylate-rich element (ARE) motifs are cis-acting elements present in the 3′ untranslated region of mRNA transcripts that encode many inflammation- and cancer-associated genes. The TIS11 family of RNA-binding proteins, composed of tristetraprolin (TTP) and butyrate response factors 1 and 2 (BRF-1 and -2), plays a critical role in regulating the expression of ARE-containing mRNAs. Through their ability to bind and target ARE-containing mRNAs for rapid degradation, this class of RNA-binding proteins serves a fundamental role in limiting the expression of a number of critical genes, thereby exerting anti-inflammatory and anti-cancer effects. Regulation of TIS11 family members occurs on a number of levels through cellular signaling events to control their transcription, mRNA turnover, phosphorylation status, cellular localization, association with other proteins, and proteosomal degradation, all of which impact TIS11 members' ability to promote ARE-mediated mRNA decay along with decay-independent functions. This review summarizes our current understanding of posttranscriptional regulation of ARE-containing gene expression by TIS11 family members and discusses their role in maintaining normal physiological processes and the pathological consequences in their absence.

Networks controlling mRNA decay in the immune system

The active control of mRNA degradation has emerged as a key regulatory mechanism required for proper gene expression in the immune system. An adenosine/uridine (AU)-rich element (ARE) is at the heart of a first regulatory system that promotes the rapid degradation of a multitude of cytokine and chemokine mRNAs. AREs serve as binding sites for a number of regulatory proteins that either destabilize or stabilize the mRNA. Several kinase pathways regulate the activity of ARE-binding proteins and thereby coordinate the expression of their target mRNAs. Small regulatory micro (mi)-RNAs represent a second system that enhances the degradation of several mRNAs encoding important components of signal transduction cascades that are activated during adaptive and innate immune responses. Specific miRNAs are important for the differentiation of T helper cells, class switch recombination in B cells, and the maturation of dendritic cells. Excitement in this area of research is fueled by the discovery of novel RNA elements and regulatory proteins that exert control over specific mRNAs, as exemplified by an endonuclease that was found to directly cleave interleukin-6 mRNA. Together, these systems make up an extensive regulatory network that controls decay rates of individual mRNAs in a precise manner and thereby orchestrates the dynamic expression of many factors essential for adaptive and innate immune responses. In this review, we provide an overview of relevant factors regulated at the level of mRNA stability, summarize RNA-binding proteins and miRNAs that control their degradation rates, and discuss signaling pathways operating within this regulatory network.

Control of cytokine mRNA expression by RNA-binding proteins and microRNAs

Cytokines are critical mediators of inflammation and host defenses. Regulation of cytokines can occur at various stages of gene expression, including transcription, mRNA export, and post- transcriptional and translational levels. Among these modes of regulation, post-transcriptional regulation has been shown to play a vital role in controlling the expression of cytokines by modulating mRNA stability. The stability of cytokine mRNAs, including TNFα, IL-6, and IL-8, has been reported to be altered by the presence of AU-rich elements (AREs) located in the 3'-untranslated regions (3'UTRs) of the mRNAs. Numerous RNA-binding proteins and microRNAs bind to these 3'UTRs to regulate the stability and/or translation of the mRNAs. Thus, this paper describes the cooperative function between RNA-binding proteins and miRNAs and how they regulate AU-rich elements containing cytokine mRNA stability/degradation and translation. These mRNA control mechanisms can potentially influence inflammation as it relates to oral biology, including periodontal diseases and oral pharyngeal cancer progression.

MAPK usage in periodontal disease progression

In periodontal disease, host recognition of bacterial constituents, including lipopolysaccharide (LPS), induces p38 MAPK activation and subsequent inflammatory cytokine expression, favoring osteoclastogenesis and increased net bone resorption in the local periodontal environment. In this paper, we discuss evidence that the p38/MAPK-activated protein kinase-2 (MK2) signaling axis is needed for periodontal disease progression: an orally administered p38α inhibitor reduced the progression of experimental periodontal bone loss by reducing inflammation and cytokine expression. Subsequently, the significance of p38 signaling was confirmed with RNA interference to attenuate MK2-reduced cytokine expression and LPS-induced alveolar bone loss. MAPK phosphatase-1 (MKP-1), a negative regulator of MAPK activation, was also critical for periodontal disease progression. In MPK-1-deficient mice, p38-sustained activation increased osteoclast formation and bone loss, whereas MKP-1 overexpression dampened p38 signaling and subsequent cytokine expression. Finally, overexpression of the p38/MK2 target RNA-binding tristetraprolin (TTP) decreased mRNA stability of key inflammatory cytokines at the posttranscriptional level, thereby protecting against periodontal inflammation. Collectively, these studies highlight the importance of p38 MAPK signaling in immune cytokine production and periodontal disease progression.

Tumor necrosis factor-α synthesis inhibitor, 3,6'-dithiothalidomide, reverses behavioral impairments induced by minimal traumatic brain injury in mice

Mild traumatic brain injury (mTBI) patients do not show clear structural brain defects and, in general, do not require hospitalization, but frequently suffer from long-lasting cognitive, behavioral and emotional difficulties. Although there is no current effective treatment or cure for mTBI, tumor necrosis factor-alpha (TNF-α), a cytokine fundamental in the systemic inflammatory process, represents a potential drug target. TNF-α levels increase after mTBI and may induce or exacerbate secondary damage to brain tissue. The present study evaluated the efficacy of the experimental TNF-α synthesis inhibitor, 3,6'-dithiothalidomide, on recovery of mice from mTBI in a closed head weight-drop model that induces an acute elevation in brain TNF-α and an impairment in cognitive performance, as assessed by the Y-maze, by novel object recognition and by passive avoidance paradigms at 72 h and 7 days after injury. These impairments were fully ameliorated in mice that received a one time administration of 3,6'-dithiothalidomide at either a low (28 mg/kg) or high (56 mg/kg) dose provided either 1 h prior to injury, or at 1 or 12 h post-injury. Together, these results implicate TNF-α as a drug target for mTBI and suggests that 3,6'-dithiothalidomide may act as a neuroprotective drug to minimize impairment.

Design, synthesis and biological assessment of novel N-substituted 3-(phthalimidin-2-yl)-2,6-dioxopiperidines and 3-substituted 2,6-dioxopiperidines for TNF-α inhibitory activity

Eight novel 2-(2,6-dioxopiperidin-3-yl)phthalimidine EM-12 dithiocarbamates 9 and 10, N-substituted 3-(phthalimidin-2-yl)-2,6-dioxopiperidines 11-14 and 3-substituted 2,6-dioxopiperidines 16 and 18 were synthesized as tumor necrosis factor-α (TNF-α) synthesis inhibitors. Synthesis involved utilization of a novel condensation approach, a one-pot reaction involving addition, iminium rearrangement and elimination, to generate the phthalimidine ring required for the creation of compounds 9-14. Agents were, thereafter, quantitatively assessed for their ability to suppress the synthesis on TNF-α in a lipopolysaccharide (LPS)-challenged mouse macrophage-like cellular screen, utilizing cultured RAW 264.7 cells. Whereas compounds 9, 14 and 16 exhibited potent TNF-α lowering activity, reducing TNF-α by up to 48% at 30 μM, compounds 12, 17 and 18 presented moderate TNF-α inhibitory action. The TNF-α lowering properties of these analogs proved more potent than that of revlimid (3) and thalidomide (1). In particular, N-dithiophthalimidomethyl-3-(phthalimidin-2-yl)-2,6-dioxopiperidine 14 not only possessed the greatest potency of the analogs to reduce TNF-α synthesis, but achieved this with minor cellular toxicity at 30 μM. The pharmacological focus of the presented compounds is towards the development of well-tolerated agents to ameliorate the neuroinflammation, that is, commonly associated with neurodegenerative disorders, epitomized by Alzheimer's disease and Parkinson's disease.

Tristetraprolin regulates interleukin-6 expression through p38 MAPK-dependent affinity changes with mRNA 3' untranslated region

Tristetraprolin (TTP) is a well-characterized, zinc finger-containing, RNA-binding protein. TTP targets tumor necrosis factor α for degradation via the 3' untranslated region (3'UTR). Although AU-rich elements (AREs) in the 3'UTR of interleukin-6 (IL-6) mRNA dictate mRNA degradation, the role of TTP in the post-transcriptional regulation of IL-6 gene expression is unclear. Here we used TTP-deficient mice to test the hypothesis that IL-6 expression is influenced by TTP. Genetic and siRNA-mediated knockdown of TTP resulted in increased IL-6 production and overexpression of TTP had the reverse effect. IL-6 and tumor necrosis factor α production were elevated after injection of IL-1β in TTP-deficient mice. Further, embryonic fibroblasts from these mice (mouse embryonic fibroblasts) exhibited greater IL-6 mRNA expression and longer half-life than wild-type mouse embryonic fibroblasts. Overexpression of TTP reduced IL-6 3'UTR luciferase reporter activity in an ARE-dependent manner. Proximal and distal regions of the 3'UTR acted synergistically to produce the full repression of TTP. Mutation-based luciferase assays show that ARE2, ARE3, and ARE4 are required for TTP-mediated repression. The constitutively activated p38-MK2 pathway abrogated TTP-mediated repression of IL-6 3'UTR reporter activity. RNA immunoprecipitation assay indicated that the deficiency of p38α resulted in the increased affinity of TTP to IL-6 mRNA. Taken together, we propose that TTP downregulates IL-6 gene expression at the post-transcriptional level by targeting ARE elements in the 3'UTR region.

Cell- and gene-based therapeutic strategies for periodontal regenerative medicine

Inflammatory periodontal diseases are a leading cause of tooth loss and are linked to multiple systemic conditions, such as cardiovascular disease and stroke. Reconstruction of the support and function of affected tooth-supporting tissues represents an important therapeutic endpoint for periodontal regenerative medicine. An improved understanding of periodontal biology coupled with current advances in scaffolding matrices has introduced novel treatments that use cell and gene therapy to enhance periodontal tissue reconstruction and its biomechanical integration. Cell and gene delivery technologies have the potential to overcome limitations associated with existing periodontal therapies, and may provide a new direction in sustainable inflammation control and more predictable tissue regeneration of supporting alveolar bone, periodontal ligament, and cementum. This review provides clinicians with the current status of these early-stage and emerging cell- and gene-based therapeutics in periodontal regenerative medicine, and introduces their future application in clinical periodontal treatment. The paper concludes with prospects on the application of cell and gene tissue engineering technologies for reconstructive periodontology.

Tristetraprolin regulates interleukin-6, which is correlated with tumor progression in patients with head and neck squamous cell carcinoma

BACKGROUND

Tumor-derived cytokines play a significant role in the progression of head and neck squamous cell carcinoma (HNSCC). Targeting proteins, such as tristetraprolin (TTP), that regulate multiple inflammatory cytokines may inhibit the progression of HNSCC. However, TTP's role in cancer is poorly understood. The goal of the current study was to determine whether TTP regulates inflammatory cytokines in patients with HNSCC.

METHODS

TTP messenger RNA (mRNA) and protein expression were determined by quantitative real-time-polymerase chain reaction (Q-RT-PCR) and Western blot analysis, respectively. mRNA stability and cytokine secretion were evaluated by quantitative RT-PCR and enzyme-linked immunoadsorbent assay, respectively, after overexpression or knockdown of TTP in HNSCC. HNSCC tissue microarrays were immunostained for interleukin-6 (IL-6) and TTP.

RESULTS

TTP expression in HNSCC cell lines was found to be inversely correlated with the secretion of IL-6, vascular endothelial growth factor (VEGF), and prostaglandin E2 (PGE(2) )(.) Knockdown of TTP increased mRNA stability and the secretion of cytokines. Conversely, overexpression of TTP in HNSCC cells led to decreased secretion of IL-6, VEGF, and PGE(2) . Immunohistochemical staining of tissue microarrays for IL-6 demonstrated that staining intensity is prognostic for poor disease-specific survival (P = .023), tumor recurrence and development of second primary tumors (P = .014), and poor overall survival (P = .019).

CONCLUSIONS

The results of the current study demonstrated that down-regulation of TTP in HNSCC enhances mRNA stability and promotes secretion of IL-6, VEGF, and PGE(2) . Furthermore, high IL-6 secretion in HNSCC tissue is a biomarker for poor prognosis. In as much as enhanced cytokine secretion is associated with poor prognosis, TTP may be a therapeutic target to reduce multiple cytokines concurrently in patients with HNSCC.

Silencing mitogen-activated protein kinase-activated protein kinase-2 arrests inflammatory bone loss

p38 mitogen-activated protein kinases (MAPKs) are critical for innate immune signaling and subsequent cytokine expression in periodontal inflammation and bone destruction. In fact, previous studies show that systemic p38 MAPK inhibitors block periodontal disease progression. However, development of p38 MAPK inhibitors with favorable toxicological profiles is difficult. Here, we report our findings regarding the contribution of the downstream p38 MAPK substrate, mitogen-activated protein kinase-activated protein kinase 2 (MK2 or MAPKAPK-2), in immune response modulation in an experimental model of pathogen-derived lipopolysaccharide (LPS)-induced periodontal bone loss. To determine whether small interfering RNA (siRNA) technology has intraoral applications, we initially validated MK2 siRNA specificity. Then, gingival tissue surrounding maxillary molars of rats was injected with MK2 siRNA or scrambled siRNA at the palatal regions of bone loss. Intraoral tissues treated with MK2 siRNA had significantly less MK2 mRNA expression compared with scrambled siRNA-treated tissues. MK2 siRNA delivery arrested LPS-induced inflammatory bone loss, decreased inflammatory infiltrate, and decreased osteoclastogenesis. This proof-of-concept study suggests a novel target using an intraoral RNA interference strategy to control periodontal inflammation.

Anti-inflammatory effect of MAPK phosphatase-1 local gene transfer in inflammatory bone loss

Alveolar bone loss associated with periodontal diseases is the result of osteoclastogenesis induced by bacterial pathogens. The mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) is a critical negative regulator of immune response as a key phosphatase capable of dephosphorylating activated MAPKs. In this study, rat macrophages transduced with recombinant adenovirus (Ad.)MKP-1 specifically dephosphorylated activated MAPKs induced by lipopolysaccharide (LPS) compared with control cells. Bone marrow macrophages from MKP-1 knockout (KO) mice exhibited higher interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α, and select chemokine compared with wild-type (WT) mice when stimulated by LPS. In addition, bone marrow cultures from MKP-1 KO mice exhibited significantly more osteoclastogenesis induced by LPS than when compared with WT mice. Importantly, MKP-1 gene transfer in bone marrow cells of MKP-1 KO mice significantly decreased IL-6, IL-10, TNF-α and chemokine levels, and formed fewer osteoclasts induced by LPS than compared with control group of cells. Furthermore, MKP-1 gene transfer in an experimental periodontal disease model attenuated bone resorption induced by LPS. Histological analysis confirmed that periodontal tissues transduced with Ad. MKP-1 exhibited less infiltrated inflammatory cells, less osteoclasts and less IL-6 than compared with rats of control groups. These studies indicate that MKP-1 is a key therapeutic target to control of inflammation-induced bone loss.

TIS11 family proteins and their roles in posttranscriptional gene regulation

Posttranscriptional regulation of gene expression of mRNAs containing adenine-uridine rich elements (AREs) in their 3′ untranslated regions is mediated by a number of different proteins that interact with these elements to either stabilise or destabilise them. The present review concerns the TPA-inducible sequence 11 (TIS11) protein family, a small family of proteins, that appears to interact with ARE-containing mRNAs and promote their degradation. This family of proteins has been extensively studied in the past decade. Studies have focussed on determining their biochemical functions, identifying their target mRNAs, and determining their roles in cell functions and diseases.