A critical regulation of Th2 cell responses by RORα in allergic asthma

Allergic asthma is a chronic inflammatory disease of the lung and the airway, which is characterized by aberrant type 2 immune responses to otherwise unharmful aeroallergens. While the central role of Th2 cells and type 2 cytokines in the pathogenesis of allergic asthma is well documented, the regulation and plasticity of Th2 cells remain incompletely understood. By using an animal model of allergic asthma in IL-4-reporter mice, we found that Th2 cells in the lung expressed higher levels of Rora than those in the lymph nodes, and that treatment with an RORα agonist SR1078 resulted in diminished Th2 cell responses in vivo. To determine the T cell-intrinsic role of RORα in allergic asthma in vivo, we established T cell-specific RORα-deficient (Cd4creRora^f/f) mice. Upon intranasal allergen challenges, Cd4creRora^f/f mice exhibited a significantly increased Th2 cells in the lungs and the airway and showed an enhanced eosinophilic inflammation compared to littermate control mice. Studies with Foxp3^YFP-creRora^f/f mice and CD8⁺ T cell depletion showed that the increased Th2 cell responses in the Cd4creRora^f/f mice were independent of Treg cells and CD8⁺ T cells. Our findings demonstrate a critical regulatory role of RORα in Th2 cells, which suggest that RORα agonists could be effective for the treatment of allergic diseases.

     

Regulation of macrophage differentiation and polarization by group IVC phospholipase A₂

Although the cellular function of group IVC phospholipase A(2) (IVC-PLA(2)) remains to be understood, the expression of IVC-PLA(2) in human monocytic THP-1 cells was increased during phorbol ester-induced macrophage differentiation. We therefore examined the role of IVC-PLA(2) in macrophage differentiation using THP-1 cells. Two THP-1 cell lines stably expressing IVC-PLA(2)-specific shRNA were established. Differentiation and maturation into macrophages on treatment with phorbol ester were facilitated by knockdown of IVC-PLA(2) without the compensatory induction of mRNA expression for other group IV and VI PLA(2)s. Furthermore, the enhancement of macrophage differentiation by IVC-PLA(2)-knockdown were abolished by treatment with lysophosphatidylcholine, a metabolite of phospholipids generated by PLA(2)-mediated hydrolysis, indicating that PLA(2) activity is necessary for the inhibition of macrophage differentiation by IVC-PLA(2). Additionally, we found that the differentiation into classically activated M1 macrophage was superior in IVC-PLA(2)-knockdown cells, whereas the differentiation into alternatively activated M2 macrophage was suppressed by IVC-PLA(2)-knockdown. These findings suggest that IVC-PLA(2) is involved in regulations of macrophage differentiation and macrophage polarization.     

Microglia-derived TNFα induces apoptosis in neural precursor cells via transcriptional activation of the Bcl-2 family member Puma

Neuroinflammation is a common feature of acute neurological conditions such as stroke and spinal cord injury, as well as neurodegenerative conditions such as Parkinson''s disease, Alzheimer''s disease, and amyotrophic lateral sclerosis. Previous studies have demonstrated that acute neuroinflammation can adversely affect the survival of neural precursor cells (NPCs) and thereby limit the capacity for regeneration and repair. However, the mechanisms by which neuroinflammatory processes induce NPC death remain unclear. Microglia are key mediators of neuroinflammation and when activated to induce a pro-inflammatory state produce a number of factors that could affect NPC survival. Importantly, in the present study we demonstrate that tumor necrosis factor α (TNFα) produced by lipopolysaccharide-activated microglia is necessary and sufficient to trigger apoptosis in mouse NPCs in vitro. Furthermore, we demonstrate that microglia-derived TNFα induces NPC apoptosis via a mitochondrial pathway regulated by the Bcl-2 family protein Bax. BH3-only proteins are known to play a key role in regulating Bax activation and we demonstrate that microglia-derived TNFα induces the expression of the BH3-only family member Puma in NPCs via an NF-κB-dependent mechanism. Specifically, we show that NF-κB is activated in NPCs treated with conditioned media from activated microglia and that Puma induction and NPC apoptosis is blocked by the NF-κB inhibitor BAY-117082. Importantly, we have determined that NPC apoptosis induced by activated microglia-derived TNFα is attenuated in Puma-deficient NPCs, indicating that Puma induction is required for NPC death. Consistent with this, we demonstrate that Puma-deficient NPCs exhibit an ∼13-fold increase in survival as compared with wild-type NPCs following transplantation into the inflammatory environment of the injured spinal cord in vivo. In summary, we have identified a key signaling pathway that regulates neuroinflammation induced apoptosis in NPCs in vitro and in vivo that could be targeted to promote regeneration and repair in diverse neurological conditions.     

Subcellular localization and lysophospholipase/transacylation activities of human group IVC phospholipase A2 (cPLA2γ)

cPLA2γ was identified as an ortholog of cPLA2α, which is a key enzyme in eicosanoid production. cPLA2γ was reported to be located in endoplasmic reticulum (ER) and mitochondria and to have lysophospholipase activity beside phospholipase A2 (PLA2) activity. However, subcellular localization, mechanism of membrane binding, regulation and physiological function have not been fully established. In the present study, we examined the subcellular localization and enzymatic properties of cPLA2γ with C-terminal FLAG-tag. We found that cPLA2γ was located not only in ER but also mitochondria even in the absence of the prenylation. Purified recombinant cPLA2γ catalyzed an acyltransferase reaction from one molecule of lysophosphatidylcholine (LPC) to another, forming phosphatidylcholine (PC). LPC or lysophosphatidylethanolamine acted as acyl donor and acceptor, but lysophosphatidylserine, lysophosphatidylinositol and lysophosphatidic acid (LPA) did not. PC and phosphatidylethanolamine (PE) also acted as weak acyl donors. Reaction conditions changed the balance of lysophospholipase and transacylation activities, with addition of LPA/PA, pH > 8, and elevated temperature markedly increasing transacylation activity; this suggests that lysophospholipase/transacylation activities of cPLA2γ may be regulated by various factors. As lysophospholipids are known to accumulate in ischemia heart and to induce arryhthmia, the cPLA2γ that is abundant in heart may have a protective role through clearance of lysophospholipids by its transacylation activity.     

A novel regulation of VEGF expression by HIF-1α and STAT3 in HDM2 transfected prostate cancer cells

On the basis of increasing roles for HDM2 oncoprotein in cancer growth and progression, we speculated that HDM2 might play a major role in hypoxia-induced metastatic process. For verification of this hypothesis, wild-type LNCaP prostate cancer cells and HDM2 transfected LNCaP-MST (HDM2 stably transfected) cells were studied. The data obtained from our experiments revealed that the HDM2 transfected LNCaP-MST cells possessed an ability to multiply rapidly and show distinct morphological features compared to non-transfected LNCaP cells. During exposures to hypoxia HDM2 expression in the LNCaP and LNCaP-MST cells was significantly higher compared to the normoxic levels. The LNCaP-MST cells also expressed higher levels of HIF-1α (hypoxia-inducible factor-1α) and p-STAT3 even under the normoxic conditions compared to the non-transfected cells. The HIF-1α and p-STAT3 expressions were increased several fold when the cells were subjected to hypoxic conditions. The HIF-1α and p-STAT3 protein expressions observed in HDM2 transfected LNCaP-MST cells were 20 and 15 folds higher, respectively, compared to the non-transfected wild-type LNCaP cells. These results demonstrate that HDM2 may have an important regulatory role in mediating the HIF-1α and p-STAT3 protein expression during both normoxic and hypoxic conditions. Furthermore, the vascular endothelial growth factor (VEGF) expression that is typically regulated by HIF-1α and p-STAT3 was also increased significantly by 136% (P < 0.01) after HDM2 transfection. The overall results point towards a novel ability of HDM2 in regulating HIF-1α and p-STAT3 levels even in normoxic conditions that eventually lead to an up-regulation of VEGF expression.     

Involvement of diacylglycerol produced by phospholipase D activation in Aβ-induced reduction of sAPPα secretion in SH-SY5Y neuroblastoma cells

We previously reported that the thiol proteinase inhibitor, E-64-d, ameliorated amyloid β (Aβ)-induced reduction of soluble amyloid precursor protein α (sAPPα) secretion by reversing ceramide-induced protein kinase C down-regulation in SH-SY5Y neuroblastoma cells. In the present study, we showed that Aβ (1–42) peptide enhanced diacylglycerol (DAG) production by phospholipase D (PLD) activation in these cells. We subsequently examined whether PLD was involved in Aβ-induced reduction of sAPPα secretion and showed that 2 μM CAY10593, which selectively inhibits PLD2, ameliorated reduction of sAPPα secretion, whereas 50 nM CAY10593, which selectively inhibits PLD1, did not. Moreover, 50 µM propranolol, a phosphatidic acid phosphohydrolase inhibitor, also ameliorated Aβ-induced reduction of sAPPα secretion, suggesting that DAG may be responsible for Aβ-induced reduction of sAPPα. We subsequently examined whether DAG affects sAPPα secretion and showed that a DAG analog reduced sAPPα secretion in SH-SY5Y cells. In addition, DAG enhanced ceramide production by stimulating neutral sphingomyelinase (N-SMase) activity. We previously demonstrated that Aβ stimulates N-SMase activity in SH-SY5Y cells. Here, we showed that inhibition of PLD2 by 2 μM CAY10593 suppressed Aβ-induced N-SMase activation. Taken together, the results suggest that DAG produced through the PLD pathway is involved in Aβ-induced reduction of sAPPα secretion in SH-SY5Y cells.     

Presence of an abnormal β 2-microglobulin mRNA in Daudi cells: Induction by interferon

Human α and β interferons increase the amount of class I human histocompatibility messenger RNA HLA-A, B, C and β₂-microglobulin in most human cells studied to date. This report concerns the effect of interferons on the Burkitt lymphoma-derived cell line Daudi, which does not express HLA-A, B, C antigens or β₂-microglobulin on its membrane. HLA-A, B, C messenger RNA present in Daudi cells is increased by both α and β interferons. Furthermore, we have shown that although it was not possible to detect mature β₂-microglobulin protein in the cytoplasm or on the cell membrane of Daudi cells, a poly A⁺ messenger RNA is present in Daudi cells, which hybridizes with a cDNA clone specific for human β²-microglobulin. This abnormal messenger RNA is, however, increased normally by interferon. These effects were also observed with human interferon β on a variant of Daudi cells characterized by a markedly reduced sensitivity to anti-proliferative and anti-cellular effects of human interferon α.[/p]     

Induction of placental alkaline phosphatase in choriocarcinoma cells by 5-bromo-2′-deoxyuridine

Summary Growth of choriocarcinoma cells in the presence of 5-bromo-2′-deoxyuridine (BrdUrd) results in a 30- to 40-fold increase in alkaline phosphatase activity. The effect of BrdUrd is specific for phosphatase with an alkaline pH optimum. The induction by BrdUrd is probably not due to the production of an altered enzyme, since the induced enzyme resembles the basal enzyme in thermal denaturation and kinetic properties. Enzyme induction can be prevented by thymidine but not by deoxycytidine or deoxyuridine. The induction of alkaline phosphatase appears to require incorporation of the BrdUrd into cellular DNA. The presence of BrdUrd in the growth medium is not necessary for alkaline phosphatase induction in proliferating cells containing: BrdUrd-substituted genomes. However, enzyme induction and maintenance of the induced levels of alkaline phosphatase in nonproliferating cells containing BrdUrd-substituted DNA requires the presence of the analogues in the medium. The induction of alkaline phosphatase by BrdUrd in probably an indirect process.     

Hypertonic environment elicits cyclooxygenase-2-driven prostaglandin E2 generation by colon cancer cells: Role of cytosolic phospholipase A2-α and kinase signaling pathways

Cyclooxygenase (COX)-2-derived prostaglandin (PG)E₂ controls many aspects of colon cancer development, modulating from apoptosis resistance and cell proliferation to angiogenesis, invasion, and metastasis. Here, we investigated the role of different phospholipases (PL)A₂ in supplying arachidonic acid (AA) for COX-2-dependent PGE₂ generation and signaling pathways involved in activation of colon cancer cells by a physiologically relevant stimulus. To emulate the hypertonic environment found physiologically in colon, the human colon cancer cell line Caco-2 was maintained in hypertonic complete DMEM medium. Human colon cancer cell line Caco-2 exposed to a hypertonic environment responded with marked AA release, COX-2 induction and PGE₂ generation. Selective secretory (s)PLA₂ and calcium-independent (i)PLA₂ inhibitors did not modify PGE₂ generation, while either COX-2 or cytosolic (c)PLA₂ inhibitors completely inhibited PGE₂ generation. cPLA₂-α was responsible for AA supply for PGE₂ generation, but had no role in COX-2 induction. Mitogen-activated protein (MAP) kinases, ERK 1/2, p38, and JNK, participated in the signaling events that lead to PGE₂ generation by modulating AA release, but only ERK 1/2 was involved in COX-2 upregulation. Our results indicate that hypertonic stress activates PGE₂ generation by Caco-2 cells through a mechanism dependent on MAP kinase-regulated AA mobilization, increased cPLA₂-α activity, and COX-2 induction.     

The Induction of the TNFα Death Domain Signaling Pathway in Alzheimer's Disease Brain

The tumor necrosis factor- death domain pathway contributes to cellular degeneration in a variety of conditions. This study investigates the hypothesis that this death domain pathway is progressively induced in the brain during the progression of Alzheimer's disease (AD). AD cases had increased levels of proapoptotic markers including tumor necrosis factor- (TNF), TNF receptor type 1 (TNF-R1), TNF receptor–associated death domain (TRADD), and caspase-3, 2- to 10-fold higher (P < .01) than age-matched controls and 1 to 3 times higher than transitional cases. In striking contrast, potentially neuroprotective TNF receptor type 2 (TNF-R2), and Fas-associated death domain-like interleukin-1–converting enzyme (FLICE) inhibitor protein (FLIP) were decreased in AD as compared with age-matched control cases (P < .01). Overall, there was an elevation in proapoptotic elements, including a 5-fold increase in TNF-R1 and a 12-fold decrease in FLIP in AD brains. These changes may translate to increased degenerative potential because the downstream effector caspase-3 and product of the TNF pathway was also increased in parallel with enhanced TNF proapoptotic conditions. Our findings suggest that the TNF death receptor pathway and caspases are activated in the early stages of neuronal degeneration in AD.     

Adjuvant-dependent regulation of interleukin-17 expressing γδ T cells and inhibition of Th2 responses in allergic airways disease

Background

Th2 immune responses are linked primarily to mild and moderate asthma, while Th17 cells, Interleukin-17A (IL-17) and neutrophilia have been implicated in more severe forms of disease. How Th2-dependent allergic reactions are influenced by Th17 and IL-17-γδ T cells is poorly understood. In murine models, under some conditions, IL-17 promotes Th2-biased airway inflammatory responses. However, IL-17-γδ T cells have been implicated in the inhibition and resolution of allergic airway inflammation and hyperresponsiveness (AHR).

Methods

We compared airway responses in Balb/c mice sensitized to OVA with (and without) a Th2-skewing aluminum-based adjuvant and the IL-17 skewing, complete Freund’s adjuvant (CFA). AHR was measured invasively by flexiVent, while serum OVA-IgE was quantified by an enzyme immunoassay. Airway inflammatory and cytokine profiles, and cellular sources of IL-17 were assessed from bronchoalveolar lavage and/or lungs. The role of γδ T cells in these responses was addressed in OVA/CFA sensitized mice using a γδ T cell antibody.

Results

Following OVA challenge, all mice exhibited mixed eosinophilic/neutrophilic airway inflammatory profiles and elevated serum OVA-IgE. Whereas OVA/alum sensitized mice had moderate inflammation and AHR, OVA/CFA sensitized mice had significantly greater inflammation but lacked AHR. This correlated with a shift in IL-17 production from CD4⁺ to γδ T cells. Additionally, OVA/CFA sensitized mice, given a γδ TCR stimulatory antibody, showed increased frequencies of IL-17-γδ T cells and diminished airway reactivity and eosinophilia.

Conclusions

Thus, the conditions of antigen sensitization influence the profile of cells that produce IL-17, the balance of which may then modulate the airway inflammatory responses, including AHR. The possibility for IL-17-γδ T cells to reduce AHR and robust eosinophilic inflammation provides evidence that therapeutic approaches focused on stimulating and increasing airway IL-17-γδ T cells may be an effective alternative in treating steroid resistant, severe asthma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-014-0090-5) contains supplementary material, which is available to authorized users.     

Expression and activation of the oxytocin receptor in airway smooth muscle cells: Regulation by TNFα and IL-13

Background

During pregnancy asthma may remain stable, improve or worsen. The factors underlying the deleterious effect of pregnancy on asthma remain unknown. Oxytocin is a neurohypophyseal protein that regulates a number of central and peripheral responses such as uterine contractions and milk ejection. Additional evidence suggests that oxytocin regulates inflammatory processes in other tissues given the ubiquitous expression of the oxytocin receptor. The purpose of this study was to define the role of oxytocin in modulating human airway smooth muscle (HASMCs) function in the presence and absence of IL-13 and TNFα, cytokines known to be important in asthma.

Method

Expression of oxytocin receptor in cultured HASMCs was performed by real time PCR and flow cytomery assays. Responses to oxytocin was assessed by fluorimetry to detect calcium signals while isolated tracheal rings and precision cut lung slices (PCLS) were used to measure contractile responses. Finally, ELISA was used to compare oxytocin levels in the bronchoalveloar lavage (BAL) samples from healthy subjects and those with asthma.

Results

PCR analysis demonstrates that OXTR is expressed in HASMCs under basal conditions and that both interleukin (IL)-13 and tumor necrosis factor (TNFα) stimulate a time-dependent increase in OXTR expression at 6 and 18 hr. Additionally, oxytocin increases cytosolic calcium levels in fura-2-loaded HASMCs that were enhanced in cells treated for 24 hr with IL-13. Interestingly, TNFα had little effect on oxytocin-induced calcium response despite increasing receptor expression. Using isolated murine tracheal rings and PCLS, oxytocin also promoted force generation and airway narrowing. Further, oxytocin levels are detectable in bronchoalveolar lavage (BAL) fluid derived from healthy subjects as well as from those with asthma.

Conclusion

Taken together, we show that cytokines modulate the expression of functional oxytocin receptors in HASMCs suggesting a potential role for inflammation-induced changes in oxytocin receptor signaling in the regulation of airway hyper-responsiveness in asthma.