The glucocorticoid dexamethasone inhibits HIF-1α stabilization and metabolic reprogramming in lipopolysaccharide-stimulated primary macrophages

Synthetic glucocorticoids are used to treat many chronic and acute inflammatory conditions. Frequent adverse effects of prolonged exposure to glucocorticoids include disturbances of glucose homeostasis caused by changes in glucose traffic and metabolism in muscle, liver, and adipose tissues. Macrophages are important targets for the anti-inflammatory actions of glucocorticoids. These cells rely on aerobic glycolysis to support various pro-inflammatory and antimicrobial functions. Employing a potent pro-inflammatory stimulus in two commonly used model systems (mouse bone marrow-derived and human monocyte-derived macrophages), we showed that the synthetic glucocorticoid dexamethasone inhibited lipopolysaccharide-mediated activation of the hypoxia-inducible transcription factor HIF-1α, a critical driver of glycolysis. In both cell types, dexamethasone-mediated inhibition of HIF-1α reduced the expression of the glucose transporter GLUT1, which imports glucose to fuel aerobic glycolysis. Aside from this conserved response, other metabolic effects of lipopolysaccharide and dexamethasone differed between human and mouse macrophages. These findings suggest that glucocorticoids exert anti-inflammatory effects by impairing HIF-1α-dependent glucose uptake in activated macrophages. Furthermore, harmful and beneficial (anti-inflammatory) effects of glucocorticoids may have a shared mechanistic basis, depending on the alteration of glucose utilization.

Dexamethasone impairs the expression of antimicrobial mediators in lipopolysaccharide-activated primary macrophages by inhibiting both expression and function of interferon β

Glucocorticoids potently inhibit expression of many inflammatory mediators, and have been widely used to treat both acute and chronic inflammatory diseases for more than seventy years. However, they can have several unwanted effects, amongst which immunosuppression is one of the most common. Here we used microarrays and proteomic approaches to characterise the effect of dexamethasone (a synthetic glucocorticoid) on the responses of primary mouse macrophages to a potent pro-inflammatory agonist, lipopolysaccharide (LPS). Gene ontology analysis revealed that dexamethasone strongly impaired the lipopolysaccharide-induced antimicrobial response, which is thought to be driven by an autocrine feedback loop involving the type I interferon IFNβ. Indeed, dexamethasone strongly and dose-dependently inhibited the expression of IFNβ by LPS-activated macrophages. Unbiased proteomic data also revealed an inhibitory effect of dexamethasone on the IFNβ-dependent program of gene expression, with strong down-regulation of several interferon-induced antimicrobial factors. Surprisingly, dexamethasone also inhibited the expression of several antimicrobial genes in response to direct stimulation of macrophages with IFNβ. We tested a number of hypotheses based on previous publications, but found that no single mechanism could account for more than a small fraction of the broad suppressive impact of dexamethasone on macrophage type I interferon signaling, underlining the complexity of this pathway. Preliminary experiments indicated that dexamethasone exerted similar inhibitory effects on primary human monocyte-derived or alveolar macrophages.

Dual-Ligand-Functionalized Liposomes Based on Glycyrrhetinic Acid and cRGD for Hepatocellular Carcinoma Targeting and Therapy

Hepatocellular carcinoma (HCC) is one of the most common cancers, with high mortality. Chemotherapy is one of the main treatment options for HCC. However, the high toxicity and poor specificity of chemotherapeutic drugs have limited their clinical application. In this study, dual-ligand liposomes modified with glycyrrhetinic acid (GA) and cyclic arginine-glycine-aspartic acid (cRGD) (GA/cRGD-LP) were designed to target the GA receptor and αvβ3 integrin, respectively. The aim was to develop a highly selective targeted drug delivery system and further enhance the antitumor efficiency of drugs by targeting both hepatic tumor cells and vasculature. A novel lipid conjugate (mGA-DOPE) by coupling dioleoylphosphatidyl ethanolamine (DOPE) with methyl glycyrrhetinic acid (mGA) was synthesized, and its structure was confirmed. The targeting efficiency of GA/cRGD-LP by in vitro cellular uptake and ex vivo imaging was assessed. GA- and cRGD-modified doxorubicin-loaded liposomes (GA/cRGD-LP-DOX) were prepared, and their cytotoxicity in HepG2 and antitumor activity were evaluated. The results showed that the average particle size of the GA/cRGD-LP-DOX was 114 ± 4.3 nm, and the zeta potential was -32.9 ± 2.0 mV. The transmission electron microscopy images showed that the shapes of our liposomes were spherical. cGA/cRGD-LP-DOX displayed an excellent cellular uptake in both HepG2 and human umbilical vein endothelial cells. In the in vivo study, pharmacokinetic parameters indicated that cGA/cRGD-LP can prolong the circulation time of DOX in the blood. GA/cRGD-LP-DOX showed greater inhibition of tumor growth for HepG2-bearing mice than either the single-ligand-modified liposomes or nontargeted liposomes. GA/cRGD-LP-DOX displayed higher liver tumor localization than that of single-ligand-modified liposomes or free DOX. GA/cRGD-LP is a promising drug delivery system for liver cancer targeting and therapy and is worthy of further study.

An in silico approach to understanding the interaction between cardiovascular and pulmonary lymphatic dysfunction

The lung is extremely sensitive to interstitial fluid balance, yet the role of pulmonary lymphatics in lung fluid homeostasis and its interaction with cardiovascular pressures is poorly understood. In health, there is a fine balance between fluid extravasated from the pulmonary capillaries into the interstitium and the return of fluid to the circulation via the lymphatic vessels. This balance is maintained by an extremely interdependent system governed by pressures in the fluids (air and blood) and tissue (interstitium), lung motion during breathing, and the permeability of the tissues. Chronic elevation in left atrial pressure (LAP) due to left heart disease increases the capillary blood pressure. The consequent fluid accumulation in the delicate lung tissue increases its weight, decreases its compliance, and impairs gas exchange. This interdependent system is difficult, if not impossible, to study experimentally. Computational modeling provides a unique perspective to analyze fluid movement in the cardiopulmonary vasculature in health and disease. We have developed an initial in silico model of pulmonary lymphatic function using an anatomically structured model to represent ventilation and perfusion and underlying biophysical laws governing fluid transfer at the interstitium. This novel model was tested against increased LAP and noncardiogenic effects (increased permeability). The model returned physiologically reasonable values for all applications, predicting pulmonary edema when LAP reached 25 mmHg and with increased permeability.NEW & NOTEWORTHY This model presents a novel approach to understanding the interaction between cardiac dysfunction and pulmonary lymphatic function, using anatomically structured models and biophysical equations to estimate regional variation in fluid transport from blood to interstitial and lymphatic flux. This fluid transport model brings together advanced models of ventilation, perfusion, and lung mechanics to produce a detailed model of fluid transport in health and various altered pathological conditions.

Repurposing existing products to accelerate injury recovery (REPAIR) of military relevant musculoskeletal conditions

Musculoskeletal injuries (MSKIs) are a great hindrance to the readiness of the United States Armed Forces through lost duty time and reduced operational capabilities. While most musculoskeletal injuries result in return-to-duty/activity with no (functional) limitations, the healing process is often long. Long healing times coupled with the high frequency of musculoskeletal injuries make them a primary cause of lost/limited duty days. Thus, there exists an urgent, clinically unmet need for interventions to expedite tissue healing kinetics following musculoskeletal injuries to lessen their impact on military readiness and society as a whole. There exist several treatments with regulatory approval for other indications that have pro-regenerative/healing properties, but few have an approved indication for treating musculoskeletal injuries. With the immediate need for treatment options for musculoskeletal injuries, we propose a paradigm of Repurposing Existing Products to Accelerate Injury Recovery (REPAIR). Developing treatments via repurposing existing therapeutics for other indications has shown monumental advantages in both cost effectiveness and reduced time to bring to market compared to novel candidates. Thus, undertaking the needed research efforts to evaluate the effectiveness of promising REPAIR-themed candidates has the potential to enable near-term solutions for optimizing musculoskeletal injuries recovery, thereby addressing a top priority within the United States. Armed Forces. Herein, the REPAIR paradigm is presented, including example targets of opportunity as well as practical considerations for potential technical solutions for the translation of existing therapeutics into clinical practice for musculoskeletal injuries.

The impact of bilateral injuries on the pathophysiology and functional outcomes of volumetric muscle loss

Volumetric muscle loss (VML)-defined as the irrecoverable loss of skeletal muscle tissue with associated persistent functional deficits-is among the most common and highly debilitating combat-related extremity injuries. This is particularly true in cases of severe polytrauma wherein multiple extremities may be involved as a result of high energy wounding mechanisms. As such, significant investment and effort has been made toward developing a clinically viable intervention capable of restoring the form and function of the affected musculature. While these investigations conducted to date have varied with respect to the species, breed, and sex of the chosen pre-clinical in-vivo model system, the majority of these studies have been performed in unilateral injury models, an aspect which may not fully exemplify the clinical representation of the multiply injured patient. Furthermore, while various components of the basal pathophysiology of VML (e.g., fibrosis and inflammation) have been investigated, relatively little effort has focused on how the pathophysiology and efficacy of pro-regenerative technologies is altered when there are multiple VML injuries. Thus, the purpose of this study was two-fold: (1) to investigate if/how the pathophysiology of unilateral VML injuries differs from bilateral VML injuries and (2) to interrogate the effect of bilateral VML injuries on the efficacy of a well-characterized regenerative therapy, minced muscle autograft (MMG). In contrast to our hypothesis, we show that bilateral VML injuries exhibit a similar systemic inflammatory response and improved muscle functional recovery, compared to unilateral injured animals. Furthermore, MMG treatment was found to only be effective at promoting an increase in functional outcomes in unilateral VML injuries. The findings presented herein add to the growing knowledge base of the pathophysiology of VML, and, importantly, reiterate the importance of comprehensively characterizing preclinical models which are utilized for early-stage screening of putative therapies as they can directly influence the translational research pipeline.

Inflammation causes remodeling of mitochondrial cytochrome c oxidase mediated by the bifunctional gene C15orf48

Dysregulated mitochondrial function is a hallmark of immune-mediated inflammatory diseases. Cytochrome c oxidase (CcO), which mediates the rate-limiting step in mitochondrial respiration, is remodeled during development and in response to changes of oxygen availability, but there has been little study of CcO remodeling during inflammation. Here, we describe an elegant molecular switch mediated by the bifunctional transcript C15orf48, which orchestrates the substitution of the CcO subunit NDUFA4 by its paralog C15ORF48 in primary macrophages. Expression of C15orf48 is a conserved response to inflammatory signals and occurs in many immune-related pathologies. In rheumatoid arthritis, C15orf48 mRNA is elevated in peripheral monocytes and proinflammatory synovial tissue macrophages, and its expression positively correlates with disease severity and declines in remission. C15orf48 is also expressed by pathogenic macrophages in severe coronavirus disease 2019 (COVID-19). Study of a rare metabolic disease syndrome provides evidence that loss of the NDUFA4 subunit supports proinflammatory macrophage functions.

Spontaneously Resolving Joint Inflammation Is Characterised by Metabolic Agility of Fibroblast-Like Synoviocytes

Fibroblast-like synoviocytes (FLS) play an important role in maintaining joint homeostasis and orchestrating local inflammatory processes. When activated during injury or inflammation, FLS undergo transiently increased bioenergetic and biosynthetic demand. We aimed to identify metabolic changes which occur early in inflammatory disease pathogenesis which might support sustained cellular activation in persistent inflammation. We took primary human FLS from synovial biopsies of patients with very early rheumatoid arthritis (veRA) or resolving synovitis, and compared them with uninflamed control samples from the synovium of people without arthritis. Metabotypes were compared using NMR spectroscopy-based metabolomics and correlated with serum C-reactive protein levels. We measured glycolysis and oxidative phosphorylation by Seahorse analysis and assessed mitochondrial morphology by immunofluorescence. We demonstrate differences in FLS metabolism measurable after ex vivo culture, suggesting that disease-associated metabolic changes are long-lasting. We term this phenomenon 'metabolic memory'. We identify changes in cell metabolism after acute TNFα stimulation across disease groups. When compared to FLS from patients with early rheumatoid arthritis, FLS from patients with resolving synovitis have significantly elevated mitochondrial respiratory capacity in the resting state, and less fragmented mitochondrial morphology after TNFα treatment. Our findings indicate the potential to restore cell metabotypes by modulating mitochondrial function at sites of inflammation, with implications for treatment of RA and related inflammatory conditions in which fibroblasts play a role.

Three-dimensional visualisation of the feto-placental vasculature in humans and rodents

Adequate development of the feto-placental circulation is critical for placental exchange function and healthy fetal growth. Understanding the structure of this circulation and how it informs fetal outcomes is important both in the human placenta, and the rodent, a purported comparative experimental model. Vascular casting and micro-CT imaging approaches enable detailed quantification of the complex vascular relationships in the feto-circulation, and provide detailed data to parameterise in silico models. Here, to assist researchers to apply these technically challenging methods we provide detailed approaches to cast and image; 1) human placentas at the cotyledon-level, and 2) whole rodent placentas.

Mitochondria as Key Players in the Pathogenesis and Treatment of Rheumatoid Arthritis

Mitochondria are major energy-producing organelles that have central roles in cellular metabolism. They also act as important signalling hubs, and their dynamic regulation in response to stress signals helps to dictate the stress response of the cell. Rheumatoid arthritis is an inflammatory and autoimmune disease with high prevalence and complex aetiology. Mitochondrial activity affects differentiation, activation and survival of immune and non-immune cells that contribute to the pathogenesis of this disease. This review outlines what is known about the role of mitochondria in rheumatoid arthritis pathogenesis, and how current and future therapeutic strategies can function through modulation of mitochondrial activity. We also highlight areas of this topic that warrant further study. As producers of energy and of metabolites such as succinate and citrate, mitochondria help to shape the inflammatory phenotype of leukocytes during disease. Mitochondrial components can directly stimulate immune receptors by acting as damage-associated molecular patterns, which could represent an initiating factor for the development of sterile inflammation. Mitochondria are also an important source of intracellular reactive oxygen species, and facilitate the activation of the NLRP3 inflammasome, which produces cytokines linked to disease symptoms in rheumatoid arthritis. The fact that mitochondria contain their own genetic material renders them susceptible to mutation, which can propagate their dysfunction and immunostimulatory potential. Several drugs currently used for the treatment of rheumatoid arthritis regulate mitochondrial function either directly or indirectly. These actions contribute to their immunomodulatory functions, but can also lead to adverse effects. Metabolic and mitochondrial pathways are attractive targets for future anti-rheumatic drugs, however many questions still remain about the precise role of mitochondrial activity in different cell types in rheumatoid arthritis.

Essentials for aerosol delivery to term and pre-term infants

Effectively delivering pharmaceutical aerosols to the lungs of preterm and term infants represents a considerable technical challenge. Small infants are obligatory nose breathers, they have small airways, low tidal volumes and rapid respiration rates. It is ethically unacceptable to investigate aerosol deposition in vivo in newborns due to ethical concerns about the radiation exposure involved in imaging studies and drug delivery and blood draws in pharmacokinetics studies. The purpose of the work reported in this article was thus to report the use of modeling to develop an understanding of the regional deposition of aerosols in neonates and to build a theoretical basis for choosing an optimum aerosol size to maximize delivery and minimize variability. Recent data on aerosol deposition in the nasal airways of newborn term and preterm infants was coupled to an established, scalable, lung deposition model to investigate the effects of age, aerosol size and ventilation on regional airway deposition. In the term newborn infant lung deposition ranged from 25% to 35% depending on Geometric Standard Deviations (GSDs). Intrasubject variability was minimized for aerosols with larger GSD. However, mean lung deposition is reduced with increasing GSD. A compromise between maximum lung deposition and increased intersubject variability appears to be in the region of GSDs of 1.75. In the 30-week GA preterm infant lung deposition is slightly higher than in the term infant despite smaller airways and lower tidal volumes. This is likely due to the lower inhaled flow rates that are concomitant with lower lung volumes. Finally, when aerosol delivery is directly to the trachea, as it would be if delivered via an endotracheal tube there is a monotonic increase in lung deposition with increasing aerosol size with peripheral deposition peaking at 2 to 3 µm. However, practical limitations of aerosol transport through endotracheal tubes, limiting delivered aerosol size, likely caps lung deposition at around 30% to 30% of the delivered dose.

Anatomical and histological analyses reveal that tail repair is coupled with regrowth in wild-caught, juvenile American alligators (Alligator mississippiensis)

Reptiles are the only amniotes that maintain the capacity to regenerate appendages. This study presents the first anatomical and histological evidence of tail repair with regrowth in an archosaur, the American alligator. The regrown alligator tails constituted approximately 6–18% of the total body length and were morphologically distinct from original tail segments. Gross dissection, radiographs, and magnetic resonance imaging revealed that caudal vertebrae were replaced by a ventrally-positioned, unsegmented endoskeleton. This contrasts with lepidosaurs, where the regenerated tail is radially organized around a central endoskeleton. Furthermore, the regrown alligator tail lacked skeletal muscle and instead consisted of fibrous connective tissue composed of type I and type III collagen fibers. The overproduction of connective tissue shares features with mammalian wound healing or fibrosis. The lack of skeletal muscle contrasts with lizards, but shares similarities with regenerated tails in the tuatara and regenerated limbs in Xenopus adult frogs, which have a cartilaginous endoskeleton surrounded by connective tissue, but lack skeletal muscle. Overall, this study of wild-caught, juvenile American alligator tails identifies a distinct pattern of wound repair in mammals while exhibiting features in common with regeneration in lepidosaurs and amphibia.

Enhanced therapeutic efficacy of a novel colon-specific nanosystem loading emodin on DSS-induced experimental colitis

BACKGROUND

Ulcerative colitis (UC) is an intricate enteric disease with a rising incidence that is closely related to mucosa-barrier destruction, gut dysbacteriosis, and immune disorders. Emodin (1,3,8-trihydroxy-6-methyl-9,10-anthraquinone, EMO) is a natural anthraquinone derivative that occurs in many Polygonaceae plants. Its multiple pharmacological effects, including antioxidant, immune-suppressive, and anti-bacteria activities, make it a promising treatment option for UC. However, its poor solubility, extensive absorption, and metabolism in the upper gastrointestinal tract may compromise its anti-colitis effects.

PURPOSE

EMO was loaded in a colon-targeted delivery system using multifunctional biomedical materials and the enhanced anti-colitis effect involving mucosa reconstruction was investigated in this study.

METHODS

EMO-loaded Poly (DL-lactide-co-glycolide)/Eudragit^Ⓡ S100/montmorillonite nanoparticles (EMO/PSM NPs) were prepared by a versatile single-step assembly approach. The colon-specific release behavior was characterized in vitro and in vivo, and the anti-colitis effect was evaluated in dextran sulfate sodium (DSS)-induced acute colitis in mice by weight loss, disease activity index (DAI) score, colon length, histological changes, and colitis biomarkers. The integrity of the intestinal mucosal barrier was evaluated through transwell co-culture model in vitro and serum zonulin-related tight junctions and mucin2 (MUC2) in vivo.

RESULTS

EMO/PSM NPs with a desirable hydrodynamic diameter (~ 235 nm) and negative zeta potential (~ -31 mV) could prevent the premature drug release (< 4% in the first 6 h in vitro) in the upper gastrointestinal tract (GIT) and boost retention in the lower GIT and inflamed colon mucosa in vivo. Compared to free EMO-treatment of different doses in UC mice, the NPs could enhance the remedial efficacy of EMO in DAI decline, histological remission, and regulation of colitis indicators, such as myeloperoxidase (MPO), nitric oxide (NO), and glutathione (GSH). The inflammatory factors including induced nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), TNF-α, and IL-1β were suppressed by EMO/PSM NPs at both mRNA and protein levels. The obtained NPs could also promote the regeneration of the mucosal barrier via reduced fluorescein isothiocyanate (FITC)-dextran leakage in the transwell co-culture model and decreased serum zonulin levels, which was demonstrated to be associated with the upregulated tight junctions (TJs)-related proteins (claudin-2, occludin, and zo-1) and MUC2 at mRNA level. Moreover, the NPs could contribute to attenuating the liver injury caused by free EMO under excessive immune inflammation.

CONCLUSION

Our results demonstrated that EMO/PSM NPs could specifically release EMO in the diseased colon, and effectively enhance the anti-colitis effects of EMO related to intestinal barrier improvement. It can be considered as a novel potential alternative for oral colon-targeted UC therapy by increasing therapeutic efficacy and reducing side-effects.

Distinct synovial tissue macrophage subsets regulate inflammation and remission in rheumatoid arthritis

Immune-regulatory mechanisms of drug-free remission in rheumatoid arthritis (RA) are unknown. We hypothesized that synovial tissue macrophages (STM), which persist in remission, contribute to joint homeostasis. We used single-cell transcriptomics to profile 32,000 STMs and identified phenotypic changes in patients with early/active RA, treatment-refractory/active RA and RA in sustained remission. Each clinical state was characterized by different frequencies of nine discrete phenotypic clusters within four distinct STM subpopulations with diverse homeostatic, regulatory and inflammatory functions. This cellular atlas, combined with deep-phenotypic, spatial and functional analyses of synovial biopsy fluorescent activated cell sorted STMs, revealed two STM subpopulations (MerTKposTREM2high and MerTKposLYVE1pos) with unique remission transcriptomic signatures enriched in negative regulators of inflammation. These STMs were potent producers of inflammation-resolving lipid mediators and induced the repair response of synovial fibroblasts in vitro. A low proportion of MerTKpos STMs in remission was associated with increased risk of disease flare after treatment cessation. Therapeutic modulation of MerTKpos STM subpopulations could therefore be a potential treatment strategy for RA.

Transdermal delivery of 4-aminopyridine accelerates motor functional recovery and improves nerve morphology following sciatic nerve crush injury in mice

Oral 4-aminopyridine (4-AP) is clinically used for symptomatic relief in multiple sclerosis and we recently demonstrated that systemic 4-AP had previously unknown clinically-relevant effects after traumatic peripheral nerve injury including the promotion of re-myelination, improvement of nerve conductivity, and acceleration of functional recovery. We hypothesized that, instead of oral or injection administration, transdermal 4-AP (TD-4-AP) could also improve functional recovery after traumatic peripheral nerve injury. Mice with surgical traumatic peripheral nerve injury received TD-4AP or vehicle alone and were examined for skin permeability, pharmacokinetics, functional, electrophysiological, and nerve morphological properties. 4-AP showed linear pharmacokinetics and the maximum plasma 4-AP concentrations were proportional to TD-4-AP dose. While a single dose of TD-4-AP administration demonstrated rapid transient improvement in motor function, chronic TD-4-AP treatment significantly improved motor function and nerve conduction and these effects were associated with fewer degenerating axons and thicker myelin sheaths than those from vehicle controls. These findings provide direct evidence for the potential transdermal applicability of 4-AP and demonstrate that 4-AP delivered through the skin can enhance in-vivo functional recovery and nerve conduction while decreasing axonal degeneration. The animal experiments were approved by the University Committee on Animal Research (UCAR) at the University of Rochester (UCAR-2009-019) on March 31, 2017.

The Lung Physiome and virtual patient models: From morphometry to clinical translation

The understanding or prediction of specific functions of the lung can be made using compact models that have identifiable parameters and that are custom designed to the problem of interest. However, when structure contributes to function - as is the case with most lung pathologies - structure-based, biophysical models become essential. Here we describe the application of structure-based models within the lung Physiome framework to identifying and explaining patient risk in 12patients diagnosed with acute pulmonary embolism. The model integrates perfusion, ventilation, and gas exchange to predict arterial blood gases and pulmonary artery pressure in individual patient models in response to patient-specific blood clot distribution, with full or partial arterial occlusion. The necessity for a patient-specific approach with biophysical models that account for scale-specific structure and function is demonstrated.

The Confusing World of Dry Powder Inhalers: It Is All About Inspiratory Pressures, Not Inspiratory Flow Rates

Dry powder inhalers (DPIs) all have the ability to aerosolize dry powders, but they each offer different operating mechanisms and resistances to inhaled airflow. This variety has resulted in both clinician and patient confusion concerning DPI performance, use, and effectiveness. Particularly, there is a growing misconception that a single peak inspiratory flow rate (PIFR) can determine a patient's ability to use a DPI effectively, regardless of its design or airflow resistance. For this review article, we have sifted through the relevant literature concerning DPIs, inspiratory pressures, and inspiratory flow rates to provide a comprehensive and concise discussion and recommendations for DPI use. We ultimately clarify that the controlling parameter for DPI performance is not the PIFR but the negative pressure generated by the patient's inspiratory effort. A pressure drop ∼≥1 kPa (∼10 cm H₂O) with any DPI is a reasonable threshold above which a patient should receive an adequate lung dose. Overall, we explore the underlying factors controlling inspiratory pressures, flow rates and dispensing, and dispersion characteristics of the various DPIs to clarify that inspiratory pressures, not flow rates, limit and control a patient's ability to generate sufficient flow for effective DPI use.

Enhancing tristetraprolin activity reduces the severity of cigarette smoke-induced experimental chronic obstructive pulmonary disease

Objective

Chronic obstructive pulmonary disease (COPD) is a progressive disease that causes significant mortality and morbidity worldwide and is primarily caused by the inhalation of cigarette smoke (CS). Lack of effective treatments for COPD means there is an urgent need to identify new therapeutic strategies for the underlying mechanisms of pathogenesis. Tristetraprolin (TTP) encoded by the Zfp36 gene is an anti‐inflammatory protein that induces mRNA decay, especially of transcripts encoding inflammatory cytokines, including those implicated in COPD.

Methods

Here, we identify a novel protective role for TTP in CS‐induced experimental COPD using Zfp36^aa/aa mice, a genetically modified mouse strain in which endogenous TTP cannot be phosphorylated, rendering it constitutively active as an mRNA‐destabilising factor. TTP wild‐type (Zfp36^+/+) and Zfp36^aa/aa active C57BL/6J mice were exposed to CS for four days or eight weeks, and the impact on acute inflammatory responses or chronic features of COPD, respectively, was assessed.

Results

After four days of CS exposure, Zfp36^aa/aa mice had reduced numbers of airway neutrophils and lymphocytes and mRNA expression levels of cytokines compared to wild‐type controls. After eight weeks, Zfp36^aa/aa mice had reduced pulmonary inflammation, airway remodelling and emphysema‐like alveolar enlargement, and lung function was improved. We then used pharmacological treatments in vivo (protein phosphatase 2A activator, AAL_(S), and the proteasome inhibitor, bortezomib) to promote the activation and stabilisation of TTP and show that hallmark features of CS‐induced experimental COPD were ameliorated.

Conclusion

Collectively, our study provides the first evidence for the therapeutic potential of inducing TTP as a treatment for COPD.

The Role of TTP Phosphorylation in the Regulation of Inflammatory Cytokine Production by MK2/3

Tristetraprolin (TTP) is an RNA-binding protein and an essential factor of posttranscriptional repression of cytokine biosynthesis in macrophages. Its activity is temporally inhibited by LPS-induced p38^MAPK/MAPKAPK2/3-mediated phosphorylation, leading to a rapid increase in cytokine expression. We compared TTP expression and cytokine production in mouse bone marrow-derived macrophages of different genotypes: wild type, MAPKAP kinase 2 (MK2) deletion (MK2 knockout [KO]), MK2/3 double deletion (MK2/3 double KO [DKO]), TTP-S52A-S178A (TTPaa) knock-in, as well as combined MK2 KO/TTPaa and MK2/3 DKO/TTPaa. The comparisons reveal that MK2/3 are the only LPS-induced kinases for S52 and S178 of TTP and the role of MK2 and MK3 in the regulation of TNF biosynthesis is not restricted to phosphorylation of TTP at S52/S178 but includes independent processes, which could involve other TTP phosphorylations (such as S316) or other substrates of MK2/3 or p38^MAPK Furthermore, we found differences in the dependence of various cytokines on the cooperation between MK2/3 deletion and TTP mutation ex vivo. In the cecal ligation and puncture model of systemic inflammation, a dramatic decrease of cytokine production in MK2/3 DKO, TTPaa, and DKO/TTPaa mice compared with wild-type animals is observed, thus confirming the role of the MK2/3/TTP signaling axis in cytokine production also in vivo. These findings improve our understanding of this signaling axis and could be of future relevance in the treatment of inflammation.

Protein phosphatase 2A as a therapeutic target in inflammation and neurodegeneration

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric enzyme that catalyzes the selective removal of phosphate groups from protein serine and threonine residues. Emerging evidence suggests that it functions as a tumor suppressor by constraining phosphorylation-dependent signalling pathways that regulate cellular transformation and metastasis. Therefore, PP2A-activating drugs (PADs) are being actively sought and investigated as potential novel anti-cancer treatments. Here we explore the concept that PP2A also constrains inflammatory responses through its inhibitory effects on various signalling pathways, suggesting that PADs may be effective in the treatment of inflammation-mediated pathologies.

IL-33 regulates cytokine production and neutrophil recruitment via the p38 MAPK-activated kinases MK2/3

IL-33 is an IL-1-related cytokine that can act as an alarmin when released from necrotic cells. Once released, it can target various immune cells including mast cells, innate lymphoid cells and T cells to elicit a Th2-like immune response. We show here that bone marrow-derived mast cells produce IL-13, IL-6, TNF, GM-CSF, CCL3 and CCL4 in response to IL-33 stimulation. Inhibition of the p38 MAPK, or inhibition or knockout of its downstream kinases MK2 and MK3, blocked the production of these cytokines in response to IL-33. The mechanism downstream of MK2/3 was cytokine specific; however, MK2 and MK3 were able to regulate TNF and GM-CSF mRNA stability. Previous studies in macrophages have shown that MK2 regulates mRNA stability via phosphorylation of the RNA-binding protein TTP (Zfp36). The regulation of cytokine production in mast cells was, however, independent of TTP. MK2/3 were able to phosphorylate the TTP-related protein Brf1 (Zfp36 l1) in IL-33-stimulated mast cells, suggesting a mechanism by which MK2/3 might control mRNA stability in these cells. In line with its ability to regulate in vitro IL-33-stimulated cytokine production, double knockout of MK2 and 3 in mice prevented neutrophil recruitment following intraperitoneal injection of IL-33.

Review: Synovial Cell Metabolism and Chronic Inflammation in Rheumatoid Arthritis

Metabolomic studies of body fluids show that immune-mediated inflammatory diseases such as rheumatoid arthritis (RA) are associated with metabolic disruption. This is likely to reflect the increased bioenergetic and biosynthetic demands of sustained inflammation and changes in nutrient and oxygen availability in damaged tissue. The synovial membrane lining layer is the principal site of inflammation in RA. Here, the resident cells are fibroblast-like synoviocytes (FLS) and synovial tissue macrophages, which are transformed toward overproduction of enzymes that degrade cartilage and bone and cytokines that promote immune cell infiltration. Recent studies have shown metabolic changes in both FLS and macrophages from RA patients, and these may be therapeutically targetable. However, because the origins and subset-specific functions of synoviocytes are poorly understood, and the signaling modules that control metabolic deviation in RA synovial cells are yet to be explored, significant additional research is needed to translate these findings to clinical application. Furthermore, in many inflamed tissues, different cell types can forge metabolic collaborations through solute carriers in their membranes to meet a high demand for energy or biomolecules. Such relationships are likely to exist in the synovium and have not been studied. Finally, it is not yet known whether metabolic change is a consequence of disease or whether primary changes to cellular metabolism might underlie or contribute to the pathogenesis of early-stage disease. In this review article, we collate what is known about metabolism in synovial tissue cells and highlight future directions of research in this area.

Metrics of lung tissue heterogeneity depend on BMI but not age

Altered parenchymal microstructure and complexity have been observed in older age. How to distinguish between healthy, expected changes and early signs of pathology remains poorly understood. An objective quantitative analysis of computed tomography imaging was conducted to compare mean lung density, tissue density distributions, and tissue heterogeneity in 16 subjects, 8 aged >60 yr who were gender and body mass index matched with 8 subjects aged <30 yr. Subjects had never been smokers, with no prior respiratory disease, and no radiologically identified abnormalities on computed tomography. Volume-controlled breath hold imaging acquired at 80% vital capacity (end inspiration) and 55% vital capacity (end expiration) were used for analysis. Mean lung density was not different between the age groups at end inspiration ( P = 0.806) but was larger in the younger group at end expiration (0.26 ± 0.033 vs. 0.22 ± 0.026, P = 0.008), as is expected due to increased air trapping in the older population. However, gravitational gradients of tissue density did not differ with age; the only difference in distribution of tissue density between the two age groups was a lower density in the apices of the older group at end expiration. The heterogeneity of the lung tissue assessed using two metrics showed significant differences between end inspiration and end expiration, no dependence on age, and a significant relationship with body mass index at both lung volumes when heterogeneity was calculated using quadtree decomposition but only at end expiration when using a fractal dimension. NEW & NOTEWORTHY Changes to lung tissue heterogeneity can be a normal part of aging but can also be an early indicator of disease. We use novel techniques, which have previously not been used on thoracic computed tomography imaging, to quantify lung tissue heterogeneity in young and old healthy subjects. Our results show no dependence on age but a significant correlation with body mass index.

The role of microRNAs in glucocorticoid action

Glucocorticoids (GCs) are steroids with profound anti-inflammatory and immunomodulatory activities. Synthetic GCs are widely used for managing chronic inflammatory and autoimmune conditions, as immunosuppressants in transplantation, and as anti-tumor agents in certain hematological cancers. However, prolonged GC exposure can cause adverse effects. A detailed understanding of GCs' mechanisms of action may enable harnessing of their desirable actions while minimizing harmful effects. Here, we review the impact on the GC biology of microRNAs, small non-coding RNAs that post-transcriptionally regulate gene expression. Emerging evidence indicates that microRNAs modulate GC production by the adrenal glands and the cells' responses to GCs. Furthermore, GCs influence cell proliferation, survival, and function at least in part by regulating microRNA expression. We propose that the beneficial effects of GCs may be enhanced through combination with reagents targeting specific microRNAs.

MAPK p38 regulates inflammatory gene expression via tristetraprolin: Doing good by stealth

Tristetraprolin (TTP) is an RNA-destabilizing protein that exerts profound anti-inflammatory effects by inhibiting the expression of tumour necrosis factor and many other inflammatory mediators. The mitogen-activated protein kinase (MAPK) p38 signaling pathway controls the strength and duration of inflammatory responses by regulating both the expression and function of TTP. The kinase MK2 (MAPK activated kinase 2) is activated by MAPK p38, and in turn phosphorylates TTP at two critical serine residues. One consequence of these phosphorylations is the protection of TTP from proteasome-mediated degradation. Another consequence is the loss of mRNA destabilizing activity. The control of TTP expression and function by the MAPK p38 pathway provides an elegant mechanism for coupling the on and off phases of inflammatory responses, and dictating the precise kinetics of expression of individual inflammatory mediators.

Tryptophan-Mediated Interactions between Tristetraprolin and the CNOT9 Subunit Are Required for CCR4-NOT Deadenylase Complex Recruitment

The zinc-finger protein tristetraprolin (TTP) binds to AU-rich elements present in the 3' untranslated regions of transcripts that mainly encode proteins of the inflammatory response. TTP-bound mRNAs are targeted for destruction via recruitment of the eight-subunit deadenylase complex "carbon catabolite repressor protein 4 (CCR4)-negative on TATA-less (NOT)," which catalyzes the removal of mRNA poly-(A) tails, the first obligatory step in mRNA decay. Here we show that a novel interaction between TTP and the CCR4-NOT subunit, CNOT9, is required for recruitment of the deadenylase complex. In addition to CNOT1, CNOT9 is now included in the identified CCR4-NOT subunits shown to interact with TTP. We find that both the N- and C-terminal domains of TTP are involved in an interaction with CNOT9. Through a combination of SPOT peptide array, site-directed mutagenesis, and bio-layer interferometry, we identified several conserved tryptophan residues in TTP that serve as major sites of interaction with two tryptophan-binding pockets of CNOT9, previously found to interact with another modulator GW182. We further demonstrate that these interactions are also required for recruitment of the CCR4-NOT complex and TTP-directed decay of an mRNA containing an AU-rich element in its 3'-untranslated region. Together the results reveal new molecular details for the TTP-CNOT interaction that shape an emerging mechanism whereby TTP targets inflammatory mRNAs for deadenylation and decay.

Gravity outweighs the contribution of structure to passive ventilation-perfusion matching in the supine adult human lung

Gravity and matched airway/vascular tree geometries are both hypothesized to be key contributors to ventilation-perfusion (V̇/Q̇) matching in the lung, but their relative contributions are challenging to quantify experimentally. We used a structure-based model to conduct an analysis of the relative contributions of tissue deformation (the "Slinky" effect), other gravitational mechanisms (weight of blood and gravitational gradient in tissue elastic recoil), and matched airway and arterial tree geometry to V̇/Q̇ matching and therefore to total lung oxygen exchange. Our results showed that the heterogeneity in V̇ and Q̇ were lowest and the correlation between V̇ and Q̇ was highest when the only mechanism for V̇/Q̇ matching was either tissue deformation or matched geometry. Heterogeneity in V̇ and Q̇ was highest and their correlation was poorest when all mechanisms were active (that is, at baseline). Eliminating the contribution of matched geometry did not change the correlation between V̇ and Q̇ at baseline. Despite the much larger heterogeneities in V̇ and Q̇ at baseline, the contribution of in-common (to V̇ and Q̇) gravitational mechanisms provided sufficient compensatory V̇/Q̇ matching to minimize the impact on oxygen transfer. In summary, this model predicts that during supine normal breathing under gravitational loading, passive V̇/Q̇ matching is predominantly determined by shared gravitationally induced tissue deformation, compliance distribution, and the effect of the hydrostatic pressure gradient on vessel and capillary size and blood pressures. Contribution from the matching airway and arterial tree geometries in this model is minor under normal gravity in the supine adult human lung. NEW & NOTEWORTHY We use a computational model to systematically analyze contributors to ventilation-perfusion matching in the lung. The model predicts that the multiple effects of gravity are the predominant mechanism in providing passive ventilation-perfusion matching in the supine adult human lung under normal gravitational loads, while geometric matching of airway and arterial trees plays a minor role.

Macrophage responses to lipopolysaccharide are modulated by a feedback loop involving prostaglandin E2, dual specificity phosphatase 1 and tristetraprolin

In many different cell types, pro-inflammatory agonists induce the expression of cyclooxygenase 2 (COX-2), an enzyme that catalyzes rate-limiting steps in the conversion of arachidonic acid to a variety of lipid signaling molecules, including prostaglandin E₂ (PGE₂). PGE₂ has key roles in many early inflammatory events, such as the changes of vascular function that promote or facilitate leukocyte recruitment to sites of inflammation. Depending on context, it also exerts many important anti-inflammatory effects, for example increasing the expression of the anti-inflammatory cytokine interleukin 10 (IL-10), and decreasing that of the pro-inflammatory cytokine tumor necrosis factor (TNF). The tight control of both biosynthesis of, and cellular responses to, PGE₂ are critical for the precise orchestration of the initiation and resolution of inflammatory responses. Here we describe evidence of a negative feedback loop, in which PGE₂ augments the expression of dual specificity phosphatase 1, impairs the activity of mitogen-activated protein kinase p38, increases the activity of the mRNA-destabilizing factor tristetraprolin, and thereby inhibits the expression of COX-2. The same feedback mechanism contributes to PGE₂-mediated suppression of TNF release. Engagement of the DUSP1-TTP regulatory axis by PGE₂ is likely to contribute to the switch between initiation and resolution phases of inflammation.

TNF superfamily members promote hepatitis C virus entry via an NF-κB and myosin light chain kinase dependent pathway

Preventing virally induced liver disease begins with an understanding of the host factors that define susceptibility to infection. Hepatitis C virus (HCV) is a global health issue, with an estimated 170 million infected individuals at risk of developing liver disease including fibrosis and hepatocellular carcinoma. The liver is the major reservoir supporting HCV replication and this hepatocellular tropism is defined by HCV engagement of cellular entry receptors. Hepatocytes are polarized in vivo and this barrier function limits HCV entry. We previously reported that activated macrophages promote HCV entry into polarized hepatocytes via a TNF-α-dependent process; however, the underlying mechanism was not defined. In this study, we show that several TNF superfamily members, including TNF-α, TNF-β, TWEAK and LIGHT, promote HCV entry via NF-κB-mediated activation of myosin light chain kinase (MLCK) and disruption of tight junctions. These observations support a model where HCV hijacks an inflammatory immune response to stimulate infection and uncovers a role for NF-κB-MLCK signalling in maintaining hepatocellular tight junctions.

The RNA-binding protein Tristetraprolin (TTP) is a critical negative regulator of the NLRP3 inflammasome

The NLRP3 inflammasome is a central regulator of inflammation in many common diseases, including atherosclerosis and type 2 diabetes, driving the production of pro-inflammatory mediators such as IL-1β and IL-18. Due to its function as an inflammatory gatekeeper, expression and activation of NLRP3 need to be tightly regulated. In this study, we highlight novel post-transcriptional mechanisms that can modulate NLRP3 expression. We have identified the RNA-binding protein Tristetraprolin (TTP) as a negative regulator of NLRP3 in human macrophages. TTP targets AU-rich elements in the NLRP3 3'-untranslated region (UTR) and represses NLRP3 expression. Knocking down TTP in primary macrophages leads to an increased induction of NLRP3 by LPS, which is also accompanied by increased Caspase-1 and IL-1β cleavage upon NLRP3, but not AIM2 or NLRC4 inflammasome activation. Furthermore, we found that human NLRP3 can be alternatively polyadenylated, producing a short 3'-UTR isoform that excludes regulatory elements, including the TTP- and miRNA-223-binding sites. Because TTP also represses IL-1β expression, it is a dual inhibitor of the IL-1β system, regulating expression of the cytokine and the upstream controller NLRP3.

Priming in response to pro-inflammatory cytokines is a feature of adult synovial but not dermal fibroblasts

Background

It has been hypothesized that chronic inflammatory diseases such as rheumatoid arthritis (RA) may be caused by a failure of negative feedback mechanisms. This study sought to examine negative feedback mechanisms in fibroblast-like synoviocytes (FLS), one of the most abundant cell types in the joint. We hypothesized that prior exposure of healthy FLS to an inflammatory stimulus would attenuate their responses to a second inflammatory stimulus, in the same way that negative feedback mechanisms desensitize macrophages to repeated stimulation by lipopolysaccharide. We further hypothesized that such negative feedback mechanisms would be defective in FLS derived from the joints in RA.

Methods

Synovial fibroblasts and dermal fibroblasts from non-inflamed joints and joints affected by RA and a fibroblast cell line from neonatal foreskin were stimulated twice with tumour necrosis factor (TNF) α or interleukin (IL)-1α, with a 24-h rest period between the two 24-h stimulations. Differences between response to the first and second dose of cytokine were examined by assessing secretion of inflammatory factors and intracellular signalling activity.

Results

FLS from both non-inflamed joints and joints affected by RA mounted an augmented response to re-stimulation. This response was site-specific, as primary dermal fibroblasts did not alter their response between doses. The fibroblast priming was also gene-specific and transient. Assessment of signalling events and nuclear localization showed prolonged activation of nuclear factor (NF)-κB during the second stimulation.

Conclusion

This study aimed to examine mechanisms of negative regulation of inflammatory responses in FLS. Instead, we found a pro-inflammatory stromal memory in FLS obtained from both non-inflamed joints and joints affected by RA. This suggests the joint is an area at high risk of chronic inflammation, and may provide a piece in the puzzle of how chronic inflammation is established in RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1248-6) contains supplementary material, which is available to authorized users.

The phosphorylated form of FTY720 activates PP2A, represses inflammation and is devoid of S1P agonism in A549 lung epithelial cells

Protein phosphatase 2A (PP2A) activity can be enhanced pharmacologically by PP2A-activating drugs (PADs). The sphingosine analog FTY720 is the best known PAD and we have shown that FTY720 represses production of pro-inflammatory cytokines responsible for respiratory disease pathogenesis. Whether its phosphorylated form, FTY720-P, also enhances PP2A activity independently of the sphingosine 1-phosphate (S1P) pathway was unknown. Herein, we show that FTY720-P enhances TNF-induced PP2A phosphatase activity and significantly represses TNF-induced interleukin 6 (IL-6) and IL-8 mRNA expression and protein secretion from A549 lung epithelial cells. Comparing FTY720 and FTY720-P with S1P, we show that unlike S1P, the sphingosine analogs do not induce cytokine production on their own. In fact, FTY720 and FTY720-P significantly repress S1P-induced IL-6 and IL-8 production. We then examined their impact on expression of cyclooxygenase 2 (COX-2) and resultant prostaglandin E2 (PGE2) production. S1P did not increase production of this pro-inflammatory enzyme because COX-2 mRNA gene expression is NF-κB-dependent, and unlike TNF, S1P did not activate NF-κB. However, TNF-induced COX-2 mRNA expression and PGE2 secretion is repressed by FTY720 and FTY720-P. Hence, FTY720-P enhances PP2A activity and that PADs can repress production of pro-inflammatory cytokines and enzymes in A549 lung epithelial cells in a manner devoid of S1P agonism.

Treatment of inflammatory arthritis via targeting of tristetraprolin, a master regulator of pro-inflammatory gene expression

OBJECTIVES

Tristetraprolin (TTP), a negative regulator of many pro-inflammatory genes, is strongly expressed in rheumatoid synovial cells. The mitogen-activated protein kinase (MAPK) p38 pathway mediates the inactivation of TTP via phosphorylation of two serine residues. We wished to test the hypothesis that these phosphorylations contribute to the development of inflammatory arthritis, and that, conversely, joint inflammation may be inhibited by promoting the dephosphorylation and activation of TTP.

METHODS

The expression of TTP and its relationship with MAPK p38 activity were examined in non-inflamed and rheumatoid arthritis (RA) synovial tissue. Experimental arthritis was induced in a genetically modified mouse strain, in which endogenous TTP cannot be phosphorylated and inactivated. In vitro and in vivo experiments were performed to test anti-inflammatory effects of compounds that activate the protein phosphatase 2A (PP2A) and promote dephosphorylation of TTP.

RESULTS

TTP expression was significantly higher in RA than non-inflamed synovium, detected in macrophages, vascular endothelial cells and some fibroblasts and co-localised with MAPK p38 activation. Substitution of TTP phosphorylation sites conferred dramatic protection against inflammatory arthritis in mice. Two distinct PP2A agonists also reduced inflammation and prevented bone erosion. In vitro anti-inflammatory effects of PP2A agonism were mediated by TTP activation.

CONCLUSIONS

The phosphorylation state of TTP is a critical determinant of inflammatory responses, and a tractable target for novel anti-inflammatory treatments.

Activating protein phosphatase 2A (PP2A) enhances tristetraprolin (TTP) anti-inflammatory function in A549 lung epithelial cells

Chronic respiratory diseases are driven by inflammation, but some clinical conditions (severe asthma, COPD) are refractory to conventional anti-inflammatory therapies. Thus, novel anti-inflammatory strategies are necessary. The mRNA destabilizing protein, tristetraprolin (TTP), is an anti-inflammatory molecule that functions to induce mRNA decay of cytokines that drive pathogenesis of respiratory disorders. TTP is regulated by phosphorylation and protein phosphatase 2A (PP2A) is responsible for dephosphorylating (and hence activating) TTP, amongst other targets. PP2A is activated by small molecules, FTY720 and AAL(S), and in this study we examine whether these compounds repress cytokine production in a cellular model of airway inflammation using A549 lung epithelial cells stimulated with tumor necrosis factor α (TNFα) in vitro. PP2A activators significantly increase TNFα-induced PP2A activity and inhibit mRNA expression and protein secretion of interleukin 8 (IL-8) and IL-6; two key pro-inflammatory cytokines implicated in respiratory disease and TTP targets. The effect of PP2A activators is not via an increase in TNFα-induced TTP mRNA expression; instead we demonstrate a link between PP2A activation and TTP anti-inflammatory function by showing that specific knockdown of TTP with siRNA reversed the repression of TNFα-induced IL-8 and IL-6 mRNA expression and protein secretion by FTY720. Therefore we propose that PP2A activators affect the dynamic equilibrium regulating TTP; shifting the equilibrium from phosphorylated (inactive) towards unphosphorylated (active) but unstable TTP. PP2A activators boost the anti-inflammatory function of TTP and have implications for future pharmacotherapeutic strategies to combat inflammation in respiratory disease.

Dual-Specificity Phosphatase 1 and Tristetraprolin Cooperate To Regulate Macrophage Responses to Lipopolysaccharide

Dual-specificity phosphatase (DUSP) 1 dephosphorylates and inactivates members of the MAPK superfamily, in particular, JNKs, p38α, and p38β MAPKs. It functions as an essential negative regulator of innate immune responses, hence disruption of the Dusp1 gene renders mice extremely sensitive to a wide variety of experimental inflammatory challenges. The principal mechanisms behind the overexpression of inflammatory mediators by Dusp1(-/-) cells are not known. In this study, we use a genetic approach to identify an important mechanism of action of DUSP1, involving the modulation of the activity of the mRNA-destabilizing protein tristetraprolin. This mechanism is key to the control of essential early mediators of inflammation, TNF, CXCL1, and CXCL2, as well as the anti-inflammatory cytokine IL-10. The same mechanism also contributes to the regulation of a large number of transcripts induced by treatment of macrophages with LPS. These findings demonstrate that modulation of the phosphorylation status of tristetraprolin is an important physiological mechanism by which innate immune responses can be controlled.

Dominant Suppression of Inflammation via Targeted Mutation of the mRNA Destabilizing Protein Tristetraprolin

In myeloid cells, the mRNA-destabilizing protein tristetraprolin (TTP) is induced and extensively phosphorylated in response to LPS. To investigate the role of two specific phosphorylations, at serines 52 and 178, we created a mouse strain in which those residues were replaced by nonphosphorylatable alanine residues. The mutant form of TTP was constitutively degraded by the proteasome and therefore expressed at low levels, yet it functioned as a potent mRNA destabilizing factor and inhibitor of the expression of many inflammatory mediators. Mice expressing only the mutant form of TTP were healthy and fertile, and their systemic inflammatory responses to LPS were strongly attenuated. Adaptive immune responses and protection against infection by Salmonella typhimurium were spared. A single allele encoding the mutant form of TTP was sufficient for enhanced mRNA degradation and underexpression of inflammatory mediators. Therefore, the equilibrium between unphosphorylated and phosphorylated TTP is a critical determinant of the inflammatory response, and manipulation of this equilibrium may be a means of treating inflammatory pathologies.

Basal protein phosphatase 2A activity restrains cytokine expression: role for MAPKs and tristetraprolin

PP2A is a master controller of multiple inflammatory signaling pathways. It is a target in asthma; however the molecular mechanisms by which PP2A controls inflammation warrant further investigation. In A549 lung epithelial cells in vitro we show that inhibition of basal PP2A activity by okadaic acid (OA) releases restraint on MAPKs and thereby increases MAPK-mediated pro-asthmatic cytokines, including IL-6 and IL-8. Notably, PP2A inhibition also impacts on the anti-inflammatory protein - tristetraprolin (TTP), a destabilizing RNA binding protein regulated at multiple levels by p38 MAPK. Although PP2A inhibition increases TTP mRNA expression, resultant TTP protein builds up in the hyperphosphorylated inactive form. Thus, when PP2A activity is repressed, pro-inflammatory cytokines increase and anti-inflammatory proteins are rendered inactive. Importantly, these effects can be reversed by the PP2A activators FTY720 and AAL(s), or more specifically by overexpression of the PP2A catalytic subunit (PP2A-C). Moreover, PP2A plays an important role in cytokine expression in cells stimulated with TNFα; as inhibition of PP2A with OA or PP2A-C siRNA results in significant increases in cytokine production. Collectively, these data reveal the molecular mechanisms of PP2A regulation and highlight the potential of boosting the power of endogenous phosphatases as novel anti-inflammatory strategies to combat asthmatic inflammation.

Multiscale modelling of the feto-placental vasculature

The placenta provides all the nutrients required for the fetus through pregnancy. It develops dynamically, and, to avoid rejection of the fetus, there is no mixing of fetal and maternal blood; rather, the branched placental villi 'bathe' in blood supplied from the uterine arteries. Within the villi, the feto-placental vasculature also develops a complex branching structure in order to maximize exchange between the placental and maternal circulations. To understand the development of the placenta, we must translate functional information across spatial scales including the interaction between macro- and micro-scale haemodynamics and account for the effects of a dynamically and rapidly changing structure through the time course of pregnancy. Here, we present steps towards an anatomically based and multiscale approach to modelling the feto-placental circulation. We assess the effect of the location of cord insertion on feto-placental blood flow resistance and flow heterogeneity and show that, although cord insertion does not appear to directly influence feto-placental resistance, the heterogeneity of flow in the placenta is predicted to increase from a 19.4% coefficient of variation with central cord insertion to 23.3% when the cord is inserted 2 cm from the edge of the placenta. Model geometries with spheroidal and ellipsoidal shapes, but the same volume, showed no significant differences in flow resistance or heterogeneity, implying that normal asymmetry in shape does not affect placental efficiency. However, the size and number of small capillary vessels is predicted to have a large effect on feto-placental resistance and flow heterogeneity. Using this new model as an example, we highlight the importance of taking an integrated multi-disciplinary and multiscale approach to understand development of the placenta.

Temporal regulation of cytokine mRNA expression by tristetraprolin: dynamic control by p38 MAPK and MKP-1

Cytokines drive many inflammatory diseases, including asthma. Understanding the molecular mechanisms responsible for cytokine secretion will allow us to develop novel strategies to repress inflammation in the future. Harnessing the power of endogenous anti-inflammatory proteins is one such strategy. In this study, we investigate the p38 MAPK-mediated regulatory interaction of two anti-inflammatory proteins, mitogen-activated protein kinase phosphatase 1 (MKP-1) and tristetraprolin (TTP), in the context of asthmatic inflammation. Using primary cultures of airway smooth muscle cells in vitro, we explored the temporal regulation of IL-6 cytokine mRNA expression upon stimulation with TNF-α. Intriguingly, the temporal profile of mRNA expression was biphasic. This was not due to COX-2-derived prostanoid upregulation, increased expression of NLRP3 inflammasome components, or upregulation of the cognate receptor for TNF-α-TNFR1. Rather, the biphasic nature of TNF-α-induced IL-6 mRNA expression was regulated temporally by the RNA-destabilizing molecule, TTP. Importantly, TTP function is controlled by p38 MAPK, and our study reveals that its expression in airway smooth muscle cells is p38 MAPK-dependent and its anti-inflammatory activity is also controlled by p38 MAPK-mediated phosphorylation. MKP-1 is a MAPK deactivator; thus, by controlling p38 MAPK phosphorylation status in a temporally distinct manner, MKP-1 ensures that TTP is expressed and made functional at precisely the correct time to repress cytokine expression. Together, p38 MAPK, MKP-1, and TTP may form a regulatory network that exerts significant control on cytokine secretion in proasthmatic inflammation through precise temporal signaling.

Nonclassical Ly6C(-) monocytes drive the development of inflammatory arthritis in mice

Different subsets and/or polarized phenotypes of monocytes and macrophages may play distinct roles during the development and resolution of inflammation. Here, we demonstrate in a murine model of rheumatoid arthritis that nonclassical Ly6C(-) monocytes are required for the initiation and progression of sterile joint inflammation. Moreover, nonclassical Ly6C(-) monocytes differentiate into inflammatory macrophages (M1), which drive disease pathogenesis and display plasticity during the resolution phase. During the development of arthritis, these cells polarize toward an alternatively activated phenotype (M2), promoting the resolution of joint inflammation. The influx of Ly6C(-) monocytes and their subsequent classical and then alternative activation occurs without changes in synovial tissue-resident macrophages, which express markers of M2 polarization throughout the course of the arthritis and attenuate joint inflammation during the initiation phase. These data suggest that circulating Ly6C(-) monocytes recruited to the joint upon injury orchestrate the development and resolution of autoimmune joint inflammation.

Role of mitogen-activated protein kinase phosphatase-1 in corticosteroid insensitivity of chronic oxidant lung injury

Oxidative stress plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and in the induction of corticosteroid (CS) insensitivity. Chronic ozone exposure leads to a model of COPD with lung inflammation and emphysema. Mitogen-activated protein kinase phosphatase-1 (MKP-1) may underlie CS insensitivity in COPD. We determined the role played by MKP-1 by studying the effect of corticosteroids in wild-type C57/BL6J and MKP-1^−/− mice after chronic ozone exposure. Mice were exposed to ozone (3 ppm, 3 h) 12 times over 6 weeks. Dexamethasone (0.1 or 2 mg/kg; intraperitoneally) was administered before each exposure. Mice were studied 24 h after final exposure. In ozone-exposed C57/BL6J mice, bronchial hyperresponsiveness (BHR) was not inhibited by both doses of dexamethasone, but in MKP-1^−/− mice, there was a small inhibition by high dose dexamethasone (2 mg/kg). There was an increase in mean linear intercept after chronic ozone exposure in both strains which was CS-insensitive. There was lesser inflammation after low dose of dexamethasone in MKP-1^−/− mice compared to C57/Bl6J mice. Epithelial and collagen areas were modulated in ozone-exposed MKP-1^−/− mice treated with dexamethasone compared to C57/Bl6J mice. MKP-1 regulated the expression of MMP-12, IL-13 and KC induced by ozone but did not alter dexamethasone׳s effects. Bronchial hyperresponsiveness, lung inflammation and emphySEMa after chronic exposure are CS-insensitive, and the contribution of MKP-1 to CS sensitivity in this model was negligible.

Hypoxic pulmonary vasoconstriction as a contributor to response in acute pulmonary embolism

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive response unique to the lung whereby blood flow is diverted away from areas of low alveolar oxygen to improve ventilation-perfusion matching and resultant gas exchange. Some previous experimental studies have suggested that the HPV response to hypoxia is blunted in acute pulmonary embolism (APE), while others have concluded that HPV contributes to elevated pulmonary blood pressures in APE. To understand these contradictory observations, we have used a structure-based computational model of integrated lung function in 10 subjects to study the impact of HPV on pulmonary hemodynamics and gas exchange in the presence of regional arterial occlusion. The integrated model includes an experimentally-derived model for HPV. Its function is validated against measurements of pulmonary vascular resistance in normal subjects at four levels of inspired oxygen. Our results show that the apparently disparate observations of previous studies can be explained within a single model: the model predicts that HPV increases mean pulmonary artery pressure in APE (by 8.2 ± 7.0% in these subjects), and concurrently shows a reduction in response to hypoxia in the subjects who have high levels of occlusion and therefore maximal HPV in normoxia.

Dual-specificity phosphatase 1-null mice exhibit spontaneous osteolytic disease and enhanced inflammatory osteolysis in experimental arthritis

OBJECTIVE

Bone formation and destruction are usually tightly linked; however, in disorders such as rheumatoid arthritis, periodontal disease, and osteoporosis, elevated osteoclast activity leads to bone destruction. Osteoclast formation and activation are controlled by many signaling pathways, including p38 MAPK. Dual-specificity phosphatase 1 (DUSP-1) is a factor involved in the negative regulation of p38 MAPK. The purpose of this study was to examine the effect of Dusp1 deficiency on bone destruction.

METHODS

Penetrance, onset, and severity of collagen-induced arthritis were recorded in DUSP-1+/+ and DUSP-1-/- mice. Bone destruction was assessed by histologic and micro-computed tomographic examination of the joints. The in vitro formation and activation of osteoclasts from DUSP-1+/+ and DUSP-1-/- precursors were assessed in the absence or presence of tumor necrosis factor (TNF).

RESULTS

The formation and activation of osteoclasts in vitro in the presence of TNF were enhanced by Dusp1 gene disruption. DUSP-1-/- mice exhibited higher penetrance, earlier onset, and increased severity of experimental arthritis, accompanied by greater numbers of osteoclasts in inflamed joints and more extensive loss of bone. A DUSP-1-/- mouse colony of mixed genetic background also demonstrated striking spontaneous osteolytic destruction of distal phalanges.

CONCLUSION

DUSP-1 is a critical regulator of osteoclast activity and limits bone destruction in an experimental model of rheumatoid arthritis. Defects in the expression or activity of DUSP1 in humans may correlate with a propensity to develop osteolytic lesions in arthritis.

Inflammatory regulation of glucocorticoid metabolism in mesenchymal stromal cells

Objective

Tissue glucocorticoid (GC) levels are regulated by the GC-activating enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). This enzyme is expressed in cells and tissues arising from mesenchymal stromal cells. Proinflammatory cytokines dramatically increase expression of 11β-HSD1 in stromal cells, an effect that has been implicated in inflammatory arthritis, osteoporosis, obesity, and myopathy. Additionally, GCs act synergistically with proinflammatory cytokines to further increase enzyme expression. The present study was undertaken to investigate the mechanisms underlying this regulation.

Methods

Gene reporter analysis, rapid amplification of complementary DNA ends (RACE), chemical inhibition experiments, and genetic disruption of intracellular signaling pathways in mouse embryonic fibroblasts (MEFs) were used to define the molecular mechanisms underlying the regulation of 11β-HSD1 expression.

Results

Gene reporter, RACE, and chemical inhibitor studies demonstrated that the increase in 11β-HSD1 expression with tumor necrosis factor α (TNFα)/interleukin-1β (IL-1β) occurred via the proximal HSD11B1 gene promoter and depended on NF-κB signaling. These findings were confirmed using MEFs with targeted disruption of NF-κB signaling, in which RelA (p65) deletion prevented TNFα/IL-1β induction of 11β-HSD1. GC treatment did not prevent TNFα-induced NF-κB nuclear translocation. The synergistic enhancement of TNFα-induced 11β-HSD1 expression with GCs was reproduced by specific inhibitors of p38 MAPK. Inhibitor and gene deletion studies indicated that the effects of GCs on p38 MAPK activity occurred primarily through induction of dual-specificity phosphatase 1 expression.

Conclusion

The mechanism by which stromal cell expression of 11β-HSD1 is regulated is novel and distinct from that in other tissues. These findings open new opportunities for development of therapeutic interventions aimed at inhibiting or stimulating local GC levels in cells of mesenchymal stromal lineage during inflammation.