A phosphosite screen identifies autocrine TGF-beta-driven activation of protein kinase R as a survival-limiting factor for eosinophils

Suppression of airway allergic eosinophilia by Hp-TGM, a helminth mimic of TGF-β

Type 2-high asthma is a chronic inflammatory disease of the airways which is increasingly prevalent in countries where helminth parasite infections are rare, and characterized by T helper 2 (Th2)-dependent accumulation of eosinophils in the lungs. Regulatory cytokines such as TGF-β can restrain inflammatory reactions, dampen allergic Th2 responses, and control eosinophil activation. The murine helminth parasite Heligmosomoides polygyrus releases a TGF-β mimic (Hp-TGM) that replicates the biological and functional properties of TGF-β despite bearing no structural similarity to the mammalian protein. Here, we investigated if Hp-TGM could alleviate allergic airway inflammation in mice exposed to Alternaria alternata allergen, house dust mite (HDM) extract or alum-adjuvanted ovalbumin protein (OVA). Intranasal administration of Hp-TGM during Alternaria exposure sharply reduced airway and lung tissue eosinophilia along with bronchoalveolar lavage fluid IL-5 and lung IL-33 cytokine levels at 24 h. The protective effect of Hp-TGM on airway eosinophilia was also obtained in the longer T-cell mediated models of HDM or OVA sensitisation with significant inhibition of eotaxin-1, IL-4 and IL-13 responses depending on the model and time-point. Hp-TGM was also protective when administered parenterally either when given at the time of allergic sensitisation or during airway allergen challenge. This project has taken the first steps in identifying the role of Hp-TGM in allergic asthma and highlighted its ability to control lung inflammation and allergic pathology. Future research will investigate the mode of action of Hp-TGM against airway allergic eosinophilia, and further explore its potential to be developed as a biotherapeutic in allergic asthma.

Design, Synthesis and Biological Evaluation of Arylpyridin-2-yl Guanidine Derivatives and Cyclic Mimetics as Novel MSK1 Inhibitors. An Application in an Asthma Model

Mitogen- and Stress-Activated Kinase 1 (MSK1) is a nuclear kinase, taking part in the activation pathway of the pro-inflammatory transcription factor NF-kB and is demonstrating a therapeutic target potential in inflammatory diseases such as asthma, psoriasis and atherosclerosis. To date, few MSK1 inhibitors were reported. In order to identify new MSK1 inhibitors, a screening of a library of low molecular weight compounds was performed, and the results highlighted the 6-phenylpyridin-2-yl guanidine (compound 1a, IC₅₀~18 µM) as a starting hit for structure-activity relationship study. Derivatives, homologues and rigid mimetics of 1a were designed, and all synthesized compounds were evaluated for their inhibitory activity towards MSK1. Among them, the non-cytotoxic 2-aminobenzimidazole 49d was the most potent at inhibiting significantly: (i) MSK1 activity, (ii) the release of IL-6 in inflammatory conditions in vitro (IC₅₀~2 µM) and (iii) the inflammatory cell recruitment to the airways in a mouse model of asthma.

Mycobacterium tuberculosis-Specific Antigen Rv3619c Effectively Alleviates Allergic Asthma in Mice

Despite significant advances, asthma remains a cause of premature death, and current treatments are suboptimal. Antigen-specific Th2 cells and their cytokines are primary mediators of the pathophysiological changes seen in asthma. Studies in animal models have shown that mycobacteria can suppress the asthma phenotype by alteration of the Th1/Th2 cytokines ratio. In this study, utilizing a Th1 delivery system to modulate the allergic airway inflammation in a Th2-driven model of asthma, we evaluated the efficacy of immunization with Mycobacterium tuberculosis-specific antigen Rv3619c, either alone or in combination with low dose dexamethasone. The rv3619c gene was cloned in an expression plasmid pGES-TH-1, expressed in Escherichia coli, and the recombinant protein Rv3619c was purified to homogeneity using affinity chromatography. Mice were immunized with the recombinant protein emulsified in Freund's Incomplete Adjuvant (IFA) alone and in combination with low dose dexamethasone, and then challenged with ovalbumin (OVA). Airway inflammation was assessed by quantifying airway cytology, histological changes and Th2 cytokine (IL-5) secretion from splenocytes. OVA-specific IgE, IgG and IgG1 from sera was assessed, as well as pERK1/2 expression in the lung tissue. Immunization with recombinant Rv3619c alone inhibited the OVA-induced increase in total cell counts, eosinophil airway cell infiltration in BAL fluid, perivascular and peribronchial inflammation and fibrosis, and goblet cell hyper/metaplasia. In addition, Rv3619c/IFA inhibited the OVA-induced IL-5 in spleen cells, OVA-specific IgE, IgG, and IgG1 levels in sera, and pERK1/2 expression in lung tissue. Immunization with Rv3619c/IFA in combination with low dose dexamethasone resulted in an enhanced effect on some but not all the asthma features. Taken together, this study demonstrates that immunization with Rv3619c/IFA, alone or in combination with dexamethasone, may be an effective treatment strategy for the prevention of asthma.

CCL11 Differentially Affects Post-Stroke Brain Injury and Neuroregeneration in Mice Depending on Age

CCL11 has recently been shown to differentially affect cell survival under various pathological conditions including stroke. Indeed, CCL11 promotes neuroregeneration in neonatal stroke mice. The impact of CCL11 on the adult ischemic brain, however, remains elusive. We therefore studied the effect of ectopic CCL11 on both adolescent (six-week) and adult (six-month) C57BL6 mice exposed to stroke. Intraperitoneal application of CCL11 significantly aggravated acute brain injury in adult mice but not in adolescent mice. Likewise, post-stroke neurological recovery after four weeks was significantly impaired in adult mice whilst CCL11 was present. On the contrary, CCL11 stimulated gliogenesis and neurogenesis in adolescent mice. Flow cytometry analysis of blood and brain samples revealed a modification of inflammation by CCL11 at subacute stages of the disease. In adolescent mice, CCL11 enhances microglial cell, B and T lymphocyte migration towards the brain, whereas only the number of B lymphocytes is increased in the adult brain. Finally, the CCL11 inhibitor SB297006 significantly reversed the aforementioned effects. Our study, for the first time, demonstrates CCL11 to be a key player in mediating secondary cell injury under stroke conditions. Interfering with this pathway, as shown for SB297006, might thus be an interesting approach for future stroke treatment paradigms.

Regulation of Innate and Adaptive Immunity by TGFβ

Immune regulation by cytokines is crucial in maintaining immune homeostasis, promoting responses to infection, resolving inflammation, and promoting immunological memory. Additionally, cytokine responses drive pathology in immune-mediated disease. A crucial cytokine in the regulation of all aspects of an immune response is transforming growth factor beta (TGFβ). Although best known as a crucial regulator of T cell responses, TGFβ plays a vital role in regulating responses mediated by virtually every innate and adaptive immune cell, including dendritic cells, B cells, NK cells, innate lymphoid cells, and granulocytes. Here, we review our current knowledge of how TGFβ regulates the immune system, highlighting the multifunctional nature of TGFβ and how its function can change depending on location and context of action.

A novel approach to understanding the role of polymorphic forms of the NR3C1 and TGF-β1 genes in the modulation of the expression of IL-5 and IL-15 mRNA in asthmatic inflammation

The aim of the present study was to identify polymorphic forms of the nuclear receptor subfamily 3, group C, member 1 (NR3C1) and transforming growth factor β1 (TGF-β1) genes and evaluate their impact on the expression levels of interleukin (IL)-5 and IL‑15 in asthma. The study was conducted on a control group consisting of 91 people (54 women and 37 men). The patient group consisted of 130 participants (86 women and 44 men). Genotyping was performed by polymerase chain reaction‑restriction fragment length polymorphism (PCR‑RFLP) and PCR‑high resolution melting (HRM) methods. Interleukin expression was measured by reverse transcription‑quantitative polymerase chain reaction. The frequency of the polymorphic forms in the analyzed group were observed to be: Tth111I (rs10052957) controls AA 0.0440, AG 0.5714, GG 0.3846, patients AA 0.1538/AG 0.4692, GG 0.3769; ER22/23EK (rs6189 /rs6190) controls AG 0.0556, GG 0.9444, patients AG 0.0385, GG 0.9615; N363S (rs6195) controls AA 0.6444, AG 0.2667, GG 0.0889, patients AA 0.7846, AG 0.1385, GG 0.0769; BclI (rs41423247) controls CC 0.0879, CG 0.5604, GG 0.3516, patients CC 0.1008, CG 0.5736, GG 0.3256; C‑509T (rs1800469) controls TT 0.0805, CT 0.6322, CC 0.2874, patients TT 0.1102, CT 0.5669, CC 0.3228. The results indicated that the C‑509T single nucleotide polymorphism (SNP) of the TGF-β1 gene contributed to an increase in the IL‑5 mRNA expression levels. The GG genotype of the N363S SNP of the NR3C1 gene was observed to result in an increase in the expression levels of IL‑15. The present study indicated that the selected SNPs of the NR3C1 and TGF‑β1 genes demonstrate a regulatory effect on the expression of IL‑5 and IL‑15. Therefore, genetic variation affects inflammation in asthma and the clinical course of the disease.

Embryonic Stem Cell Growth Factors Regulate eIF2α Phosphorylation

Growth factors and transcription factors are well known to regulate pluripotent stem cells, but less is known about translational control in stem cells. Here, we use embryonic stem cells (ESCs) to investigate a connection between ESC growth factors and eIF2α-mediated translational control (eIF2α phosphorylation promotes protein expression from mRNAs with upstream open-reading frames, or uORFs). We find abundant phosphorylated P-eIF2α (P-eIF2α) in both pluripotent mouse and human ESCs, but little P-eIF2α in ESCs triggered to differentiate. We show that the growth factors LIF (leukemia inhibitory factor) and BMP4 (bone morphogenic protein 4) both maintain P-eIF2α in mESCs, but use distinct mechanisms: LIF inhibits an eIF2α phosphatase whereas BMP4 activates an eIF2α kinase. The mRNAs encoding the pluripotency factors Nanog and c-Myc possess uORFs while Oct4 mRNA does not. We find that salubrinal, a chemical that increases eIF2α phosphorylation, promotes Nanog and c-Myc expression, but not Oct4 expression. These experiments connect ESC growth factors to eIF2α phosphorylation and suggest a chemical substitute for LIF to enhance Nanog and c-Myc expression.

Determinants of eosinophil survival and apoptotic cell death

Eosinophils (Eos) are potent inflammatory cells and abundantly present in the sputum and lung of patients with allergic asthma. During both transit to and residence in the lung, Eos contact prosurvival cytokines, particularly IL-3, IL-5 and GM-CSF, that attenuate cell death. Cytokine signaling modulates the expression and function of a number of intracellular pro- and anti-apoptotic molecules. Both intrinsic mitochondrial and extrinsic receptor-mediated pathways are affected. This article discusses the fundamental role of the extracellular and intracellular molecules that initiate and control survival decisions by human Eos and highlights the role of the cis-trans isomerase, Pin1 in controlling these processes.

SOCS3 silencing attenuates eosinophil functions in asthma patients

Eosinophils are one of the key inflammatory cells in asthma. Eosinophils can exert a wide variety of actions through expression and secretion of multiple molecules. Previously, we have demonstrated that eosinophils purified from peripheral blood from asthma patients express high levels of suppressor of cytokine signaling 3 (SOCS3). In this article, SOCS3 gene silencing in eosinophils from asthmatics has been carried out to achieve a better understanding of the suppressor function in eosinophils. SOCS3 siRNA treatment drastically reduced SOCS3 expression in eosinophils, leading to an inhibition of the regulatory transcription factors GATA-3 and FoxP3, also interleukin (IL)-10; in turn, an increased STAT3 phosphorilation was observed. Moreover, SOCS3 abrogation in eosinophils produced impaired migration, adhesion and degranulation. Therefore, SOCS3 might be regarded as an important regulator implicated in eosinophil mobilization from the bone marrow to the lungs during the asthmatic process.

Mechanisms of sustained signalling in asthma

PURPOSE OF REVIEW

The role of immunological memory formation focusing upon Th2 inflammatory responses in asthma is well supported and reviewed previously. Here, we review data supporting the establishment of a tissue-based signalling memory utilizing examples of in-vitro, in-vivo and clinical reports of sustained extracellular signal regulated kinase 1/2 (ERK1/2) activation in asthma.

RECENT FINDINGS

Endosomal recycling of receptors contributes to chronic signalling activation, presumably through increased receptor availability. This chronic signalling constitutes a bistable state and the formation of a tissue memory. The transition to chronic asthma is marked by the persistence of low-level disease severity and chronic signalling in the apparent absence of an environmental trigger.

SUMMARY

System bistability provides a mathematical explanation for a tissue-based memory. We will have to generate quantitative data about the involved biochemical reactions (substrates, products, dissociation constants of the reactions) to utilize this model. Only then will we be able to understand and interfere with a tissue memory-driven disease and curtail the persistence of asthma.

Transforming Growth Factor-β1 Antagonizes Interleukin-5 Pro-Survival Signaling by Activating Calpain-1 in Primary Human Eosinophils

BACKGROUND

Eosinophils rapidly undergo apoptosis unless exposed to prosurvival cytokines such as interleukin 5 (IL-5) or granulocyte-macrophage colony stimulating factor (GM-CSF). In vivo, eosinophils are exposed to TGF-β 1 which can induce apoptosis suggesting it may function to counteract the effects of IL-5 or GM-CSF and limit, in vivo tissue eosinophilia.

OBJECTIVE

The objective of this study was to investigate the proapoptotic effects of TGF-β alone and in combination with IL-5 on eosinophils.

METHODS

Peripheral blood eosinophil (PBEos) viability was assessed using flow cytometry after exposure to TGF-β1 and IL-5. Calpain-1 activation was determined in cell extracts by western blot analysis of endogenous substrates and with a fluorogenic α-spectrin substrate. Molecular interactions between calpain1 and calpastatin were assessed by immunoprecipitation and western blotting.

RESULTS

Physiologic concentrations of TGF-β1 significantly antagonized the prosurvival effects of IL-5. TGF-β1-induced apoptosis was suppressed by inhibitors of calpain, or its downstream target, caspase 3. TGF-β1 signaling through Smad3 was unaffected by IL-5 and was required for the pro-apoptotic effects of TGF-β1. However, IL-5 induced Akt phosphorylation was inhibited by TGF-β1 and was associated with accelerated calpain cleavage and eosinophil death.

CONCLUSION

TGF-β1 induces calpain-1 activation through antagonism of Akt which induces caspase activation and eosinophil apoptosis.

Mitogen-activated protein kinase signalling and ERK1/2 bistability in asthma

Mitogen-activated protein kinases (MAPKs) integrate signals from numerous receptors and translate these signals into cell functions. MAPKs are critical for immune cell metabolism, migration, production of pro-inflammatory mediators, survival and differentiation. We provide a concise review of the involvement of MAPK in important cells of the immune system. Certain cell functions, e.g. production of pro-inflammatory mediators resolve quickly and may require a transient MAPK activation, other processes such as cell differentiation and long-term survival may require persistent MAPK signal. The persistent MAPK signal is frequently a consequence of positive feedback loops or double negative feedback loops which perpetuate the signal after removal of an external cell stimulus. This self-perpetuated activation of a signalling circuit is a manifestation of its bistability. Bistable systems can exist in 'on' and 'off' states and both states are stable. We have demonstrated the existence of self-perpetuated activation mechanism for ERK1/2 in bronchial epithelial cells. This sustained activation of ERK1/2 supports long-term survival of these cells and primes them for cytokine transcription. ERK1/2 bistability arises from repetitive stimulation of the cell. The repeated stimulation (e.g. repeated viral infection or repeated allergen exposure) seems to be a common theme in asthma and other chronic illnesses. We thus hypothesize that the self-perpetuated ERK1/2 signal plays an important role in the pathogenesis of asthma.