Elevated receptor for activated C kinase 1 expression is involved in intracellular Ca2+ influx and potentially associated with compromised regulatory T cell function in patients with asthma

Surface Phenotype Changes and Increased Response to Oxidative Stress in CD4+CD25high T Cells

Conversion of CD4+CD25+FOXP3+ T regulatory cells (Tregs) from the immature (CD45RA+) to mature (CD45RO+) phenotype has been shown during development and allergic reactions. The relative frequencies of these Treg phenotypes and their responses to oxidative stress during development and allergic inflammation were analysed in samples from paediatric and adult subjects. The FOXP3lowCD45RA+ population was dominant in early childhood, while the percentage of FOXP3highCD45RO+ cells began increasing in the first year of life. These phenotypic changes were observed in subjects with and without asthma. Further, there was a significant increase in phosphorylated ERK1/2 (pERK1/2) protein in hydrogen peroxide (H2O2)-treated CD4+CD25high cells in adults with asthma compared with those without asthma. Increased pERK1/2 levels corresponded with increased Ca2+ response to T cell receptor stimulation. mRNA expression of peroxiredoxins declined in Tregs from adults with asthma. Finally, CD4+CD25high cells from paediatric subjects were more sensitive to oxidative stress than those from adults in vitro. The differential Treg sensitivity to oxidative stress observed in children and adults was likely dependent on phenotypic CD45 isoform switching. Increased sensitivity of Treg cells from adults with asthma to H2O2 resulted from a reduction of peroxiredoxin-2, -3, -4 and increased pERK1/2 via impaired Ca2+ response in these cells.

RACK1 plays a critical role in mast cell secretion and Ca2+ mobilization by modulating F-actin dynamics

Although RACK1 is known to act as a signaling hub in immune cells, its presence and role in mast cells (MCs) is undetermined. MC activation via antigen stimulation results in mediator release and is preceded by cytoskeleton reorganization and Ca2+ mobilization. In this study, we found that RACK1 was distributed throughout the MC cytoplasm both in vivo and in vitro. After RACK1 knockdown (KD), MCs were rounded, and the cortical F-actin was fragmented. Following antigen stimulation, in RACK1 KD MCs, there was a reduction in cortical F-actin, an increase in monomeric G-actin and a failure to organize F-actin. RACK1 KD also increased and accelerated degranulation. CD63+ secretory granules were localized in F-actin-free cortical regions in non-stimulated RACK1 KD MCs. Additionally, RACK1 KD increased antigen-stimulated Ca2+ mobilization, but attenuated antigen-stimulated depletion of ER Ca2+ stores and thapsigargin-induced Ca2+ entry. Following MC activation there was also an increase in interaction of RACK1 with Orai1 Ca2+-channels, β-actin and the actin-binding proteins vinculin and MyoVa. These results show that RACK1 is a critical regulator of actin dynamics, affecting mediator secretion and Ca2+ signaling in MCs. This article has an associated First Person interview with the first author of the paper.

Modulating oxidative stress counteracts specific antigen-induced regulatory T-cell apoptosis in mice

Treg are known to have a central role in orchestrating immune responses, but less is known about the destiny of Treg after being activated by specific Ags. This study aimed to investigate the role of superoxide dismutase, an active molecule in the regulation of oxidative stress in the body, in the prevention of Treg apoptosis induced by specific Ags. Ag-specific Tregs were isolated from the DO11.10 mouse intestine. A food allergy mouse model was developed with ovalbumin as the specific Ag and here, we observed that exposure to specific Ag induced Treg apoptosis through converting the precursor of TGF-β to its mature form inside the Tregs. Oxidative stress was induced in Tregs upon exposure to specific Ags, in which Smad3 bound the latency-associated peptide to induce its degradation, converting the TGF-β precursor to its mature form, TGF-β. Suppressing oxidative stress in Tregs alleviated the specific Ag-induced Treg apoptosis in in vitro experiments and suppressed experimental food allergy by preventing the specific Ag-induced Treg apoptosis in the intestine. In conclusion, exposure to specific Ags induces Treg apoptosis and it can be prevented by upregulating superoxide dismutase or suppressing reactive oxidative species in Tregs.

Dual role of RACK1 in airway epithelial mesenchymal transition and apoptosis

Airway epithelial apoptosis and epithelial mesenchymal transition (EMT) are two crucial components of asthma pathogenesis, concomitantly mediated by TGF‐β1. RACK1 is the downstream target gene of TGF‐β1 shown to enhancement in asthma mice in our previous study. Balb/c mice were sensitized twice and challenged with OVA every day for 7 days. Transformed human bronchial epithelial cells, BEAS‐2B cells were cultured and exposed to recombinant soluble human TGF‐β1 to induced apoptosis (30 ng/mL, 72 hours) and EMT (10 ng/mL, 48 hours) in vitro, respectively. siRNA and pharmacological inhibitors were used to evaluate the regulation of RACK1 protein in apoptosis and EMT. Western blotting analysis and immunostaining were used to detect the protein expressions in vivo and in vitro. Our data showed that RACK1 protein levels were significantly increased in OVA‐challenged mice, as well as TGF‐β1‐induced apoptosis and EMT of BEAS‐2B cells. Knockdown of RACK1 (siRACK1) significantly inhibited apoptosis and decreased TGF‐β1 up‐regulated EMT related protein levels (N‐cadherin and Snail) in vitro via suppression of JNK and Smad3 activation. Moreover, siSmad3 or siJNK impaired TGF‐β1‐induced N‐cadherin and Snail up‐regulation in vitro. Importantly, JNK gene silencing (siERK) also impaired the regulatory effect of TGF‐β1 on Smad3 activation. Our present data demonstrate that RACK1 is a concomitant regulator of TGF‐β1 induces airway apoptosis and EMT via JNK/Smad/Snail signalling axis. Our findings may provide a new insight into understanding the regulation mechanism of RACK1 in asthma pathogenesis.

Impaired Autophagy and Defective T Cell Homeostasis in Mice with T Cell-Specific Deletion of Receptor for Activated C Kinase 1

Autophagy plays a central role in maintaining T cell homeostasis. Our previous study has shown that hepatocyte-specific deficiency of receptor for activated C kinase 1 (RACK1) leads to lipid accumulation in the liver, accompanied by impaired autophagy, but its in vivo role in T cells remains unclear. Here, we report that mice with T cell-specific deletion of RACK1 exhibit normal intrathymic development of conventional T cells and regulatory T (Treg) cells but reduced numbers of peripheral CD4⁺ and CD8⁺ T cells. Such defects are cell intrinsic with impaired mitochondrial clearance, increased sensitivity to cell death, and decreased proliferation that could be explained by impaired autophagy. Furthermore, RACK1 is essential for invariant natural T cell development. In vivo, T cell-specific loss of RACK1 dampens concanavalin A-induced acute liver injury. Our data suggest that RACK1 is a key regulator of T cell homeostasis.

Developments in the field of allergy in 2014 through the eyes of Clinical and Experimental Allergy

The pathogenesis of asthma continues to be a major topic of interest to our authors with reviews and original papers on the role of viruses, mechanisms of inflammation, biomarkers, and phenotypes of asthma being major topics. A number of papers described new treatments for asthma focusing on blocking the Th2 response reflecting the fact that two decades of work in this area is finally bearing fruit. The pathogenesis of chronic rhinosinusitis is a growing area of interest, but there has been less on the genetics of airways disease than in previous years possibly reflecting the degree of rigour (and therefore a smaller body of work), with which these sorts of studies are now being undertaken. There continues to be a wide range of papers dealing with mechanisms of allergic disease ranging from clinical-based studies to basic research and the use of in vivo animal models especially mice. As before, mechanisms and new approaches to immunotherapy are common themes. Several were published in the allergens section investigating modification of allergens to increase their effectiveness and reduce the risk of adverse events. Risk factors for allergic disease was a common theme in the epidemiology section and food allergy a common theme in clinical allergy with papers on the development of protocols to induce tolerance and attempts to find biomarkers to distinguish sensitization from allergic disease. This was another exciting year for the editors, and we hope the readers of the journal.

In vivo immunotoxicity of perfluorooctane sulfonate in BALB/c mice: Identification of T-cell receptor and calcium-mediated signaling pathway disruption through gene expression profiling of the spleen

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that is used worldwide and is continuously being detected in biota and the environment, thus presenting potential threats to the ecosystem and human health. Although PFOS is highly immunotoxic, its underlying molecular mechanisms remain largely unknown. The present study examined PFOS-induced immunotoxicity in the mouse spleen and explored its underlying mechanisms by gene expression profiling. Oral exposure of male BALB/c mice for three weeks followed by one-week recovery showed that a 10 mg/kg/day PFOS exposure damaged the splenic architecture, inhibited T-cell proliferation in response to mitogen, and increased the percentages of T helper (CD3(+)CD4(+)) and cytotoxic T (CD3(+)CD8(+)) cells, despite the decrease in the absolute number of these cells. A delayed type of PFOS immunotoxicity was observed, which mainly occurred during the recovery period. Global gene expression profiling of mouse spleens and QRT-PCR analyses suggest that PFOS inhibited the expression of genes involved in cell cycle regulation and NRF2-mediated oxidative stress response, and upregulated those in TCR signaling, calcium signaling, and p38/MAPK signaling pathways. Western blot analysis confirmed that the expressions of CAMK4, THEMIS, and CD3G, which were involved in the upregulated pathways, were induced upon PFOS exposure. Acute PFOS exposure modulated calcium homoeostasis in splenocytes. These results indicate that PFOS exposure can activate TCR signaling and calcium ion influx, which provides a clue for the potential mechanism of PFOS immunotoxicity. The altered signaling pathways by PFOS treatment as revealed in the present study might facilitate in better understanding PFOS immunotoxicity and explain the association between immune disease and PFOS exposure.