Unconventional activation of PRKDC by TNF-α: deciphering its crucial role in Th1-mediated inflammation beyond DNA repair as part of the DNA-PK complex

BACKGROUND

The DNA-dependent protein kinase (DNA-PK) complex comprises a catalytic (PRKDC) and two requisite DNA-binding (Ku70/Ku80) subunits. The role of the complex in repairing double-stranded DNA breaks (DSBs) is established, but its role in inflammation, as a complex or individual subunits, remains elusive. While only ~ 1% of PRKDC is necessary for DNA repair, we reported that partial inhibition blocks asthma in mice without causing SCID.

METHODS

We investigated the central role of PRKDC in inflammation and its potential association with DNA repair. We also elucidated the relationship between inflammatory cytokines (e.g., TNF-α) and PRKDC by analyzing its connections to inflammatory kinases. Human cell lines, primary human endothelial cells, and mouse fibroblasts were used to conduct the in vitro studies. For animal studies, LPS- and oxazolone-induced mouse models of acute lung injury (ALI) and delayed-type hypersensitivity (DHT) were used. Wild-type, PRKDC+/-, or Ku70+/- mice used in this study.

RESULTS

A ~ 50% reduction in PRKDC markedly blocked TNF-α-induced expression of inflammatory factors (e.g., ICAM-1/VCAM-1). PRKDC regulates Th1-mediated inflammation, such as DHT and ALI, and its role is highly sensitive to inhibition achieved by gene heterozygosity or pharmacologically. In endothelial or epithelial cells, TNF-α promoted rapid PRKDC phosphorylation in a fashion resembling that induced by, but independent of, DSBs. Ku70 heterozygosity exerted little to no effect on ALI in mice, and whatever effect it had was associated with a specific increase in MCP-1 in the lungs and systemically. While Ku70 knockout blocked VP-16-induced PRKDC phosphorylation, it did not prevent TNF-α - induced phosphorylation of the kinase, suggesting Ku70 dispensability. Immunoprecipitation studies revealed that PRKDC transiently interacts with p38MAPK. Inhibition of p38MAPK blocked TNF-α-induced PRKDC phosphorylation. Direct phosphorylation of PRKDC by p38MAPK was demonstrated using a cell-free system.

CONCLUSIONS

This study presents compelling evidence that PRKDC functions independently of the DNA-PK complex, emphasizing its central role in Th1-mediated inflammation. The distinct functionality of PRKDC as an individual enzyme, its remarkable sensitivity to inhibition, and its phosphorylation by p38MAPK offer promising therapeutic opportunities to mitigate inflammation while sparing DNA repair processes. These findings expand our understanding of PRKDC biology and open new avenues for targeted anti-inflammatory interventions.

Microparticles in systemic sclerosis: Potential pro-inflammatory mediators and pulmonary hypertension biomarkers

BACKGROUND AND OBJECTIVE

Endothelial microparticles (EMP) are submicron vesicles released from endothelial cells. We aimed to determine the utility of EMP as biomarkers of pulmonary arterial hypertension (PAH) in systemic sclerosis (SSc) patients and the pathogenic role of microparticles (MP) in vascular inflammation.

METHODS

Levels of EMP (CD144+, CD31+, CD62E+ and CD143+) were compared between three groups (10 SSc patients with PAH, 10 SSc patients without pulmonary hypertension (no-PH) and 10 healthy age- and sex-matched controls). Human pulmonary artery endothelial cells (HPAEC) were exposed in vitro to MP obtained from SSc patients or healthy controls, and levels of cytokines and inflammatory adhesion molecules were compared.

RESULTS

CD144+ EMP were significantly higher in the SSc-PAH group compared to either the SSc-no PH or healthy controls (diagnostic accuracy 80%, P = 0.02). Compared to controls, SSc patients had higher CD31+/CD62E+ ratios, indicating larger contributions of apoptosis to EMP release (P = 0.04). Patients with limited SSc had significantly higher levels of CD143+ EMP compared to those with diffuse subtype (P = 0.008). When HPAEC were exposed to MP from SSc patients, there was a significant increase in inflammatory cytokines and adhesion molecules. Interestingly, exposure to healthy control MP caused a reduction in inflammatory markers.

CONCLUSION

EMP (particularly CD144+) are promising biomarkers of PAH in SSc but require further study. MP isolated from SSc patients induced an increase in endothelial cell inflammation and may be an important pathogenic factor in SSc.

Sulfated non-anticoagulant heparin blocks Th2-induced asthma by modulating the IL-4/signal transducer and activator of transcription 6/Janus kinase 1 pathway

BACKGROUND

The efficacy of heparins and low-MW-heparins (LMWH) against human asthma has been known for decades. However, the clinical utility of these compounds has been hampered by their anticoagulant properties. Much effort has been put into harnessing the anti-inflammatory properties of LMWH but none have been used as therapy for asthma. Sulfated-non-anticoagulant heparin (S-NACH) is an ultra-LMWH with no systemic anticoagulant effects.

OBJECTIVE

The present study explored the potential of S-NACH in blocking allergic asthma and examined the potential mechanism by which it exerts its effects.

METHODS

Acute and chronic ovalbumin-based mouse models of asthma, splenocytes, and a lung epithelial cell line were used. Mice were challenged with aerosolized ovalbumin and administered S-NACH or saline 30 min after each ovalbumin challenge.

RESULTS

Sulfated-non-anticoagulant heparin administration in mice promoted a robust reduction in airway eosinophilia, mucus production, and airway hyperresponsiveness even after chronic repeated challenges with ovalbumin. Such effects were linked to suppression of Th2 cytokines IL-4/IL-5/IL-13/GM-CSF and ovalbumin-specific IgE without any effect on IFN-γ. S-NACH also reduced lung fibrosis in mice that were chronically-exposed to ovalbumin. These protective effects of S-NACH may be attributed to modulation of the IL-4/JAK1 signal transduction pathway through an inhibition of STAT6 phosphorylation and a subsequent inhibition of GATA-3 and inducible NO synthase expression. The effect of the drug on STAT6 phosphorylation coincided with a reduction in JAK1 phosphorylation upon IL-4 treatment. The protective effects of S-NACH treatment was associated with reduction of the basal expression of the two isoforms of arginase ARG1 and ARG2 in lung epithelial cells.

CONCLUSIONS

Our study demonstrates that S-NACH constitutes an opportunity to benefit from the well-known anti-asthma properties of heparins/LMWH while bypassing the risk of bleeding. Our results show, for the first time, that such anti-asthma effects may be associated with reduction of the IL-4/JAK1/STAT6 pathway.

The catalytic subunit of DNA-PK has a unique function in inflammation independently of Ku70 and DNA repair: a new opportunity to target the enzyme without interfering with DNA repair

Our laboratory demonstrated a critical role for DNA-dependent protein kinase (DNA-PK) in asthma pathogenesis via modulating the pertinent immune responses. DNA-PK is DNA repair enzyme composed of a catalytic subunit (DNA-PKcs) and two DNA-binding subunits (Ku70 and Ku80). Human cells express high levels of DNA-PK, surprisingly such high levels do not confer increased ability to repair DNA damage. Here we show that the role of DNA-PK in promoting inflammatory responses is independent of its function in the DNA repair. We examined the effect(s) of partial depletion of Ku70 on Ovalbumin (OVA) induced lung inflammation in mouse model of the disease. Of note, depletion of Ku70 by gene heterozygosity causes deficiency in DNA-PK-dependent DNA repair. Unlike the protective effects provided by DNA-PKcs gene heterozygosity, Ku70 heterozygosity did not alter the OVA-induced eosinophilia, mucus hypersecretion, Th2 cytokines production, or OVA-specific IgE upon OVA challenge. Interestingly, Ku70 heterozygosity enhanced methacholine-induced AHR over that of WT mice. Using a cell culture system, we demonstrate that while IL-4 and TNF-α are potent inducers of DNA-PKcs, such activation did not coincide with any detectable DNA damage or repair responses. Remarkably, while Ku70−/− blocked DNA-PKcs autophosphorylation in response to the DNA damage agent, etoposide, it did not affect the kinase in response to TNFα. Our findings suggest that the mechanism by which DNA-PK functions in inflammation is completely unrelated to its role in DNA repair, thus, unraveling a completely novel function for the kinase. More importantly, this provides a window of opportunity to target DNA-PK in inflammatory diseases without interfering with DNA repair processes.

Fuelling the mechanisms of asthma: Increased fatty acid oxidation in inflammatory immune cells may represent a novel therapeutic target

BACKGROUND

Increasing evidence has shown the close link between energy metabolism and the differentiation, function, and longevity of immune cells. Chronic inflammatory conditions such as parasitic infections and cancer trigger a metabolic reprogramming from the preferential use of glucose to the up-regulation of fatty acid oxidation (FAO) in myeloid cells, including macrophages and granulocytic and monocytic myeloid-derived suppressor cells. Asthma is a chronic inflammatory condition where macrophages, eosinophils, and polymorphonuclear cells play an important role in its pathophysiology.

OBJECTIVE

We tested whether FAO might play a role in the development of asthma-like traits and whether the inhibition of this metabolic pathway could represent a novel therapeutic approach.

METHODS

OVA- and house dust mite (HDM)-induced murine asthma models were used in this study.

RESULTS

Key FAO enzymes were significantly increased in the bronchial epithelium and inflammatory immune cells infiltrating the respiratory epithelium of mice exposed to OVA or HDM. Pharmacologic inhibition of FAO significantly decreased allergen-induced airway hyperresponsiveness, decreased the number of inflammatory cells, and reduced the production of cytokines and chemokines associated with asthma.

CONCLUSIONS AND CLINICAL RELEVANCE

These novel observations suggest that allergic airway inflammation increases FAO in inflammatory cells to support the production of cytokines, chemokines, and other factors important in the development of asthma. Inhibition of FAO by re-purposing existing drugs approved for the treatment of heart disease may provide a novel therapeutic approach for the treatment of asthma.

Treatment with intranasal iloprost reduces disease manifestations in a murine model of previously established COPD

Pulmonary endothelial prostacyclin appears to be involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). The effect of treatment with a prostacyclin analog in animal models of previously established COPD is unknown. We evaluated the short- and long-term effect of iloprost on inflammation and airway hyperresponsiveness (AHR) in a murine model of COPD. Nineteen mice were exposed to LPS/elastase, followed by either three doses of intranasal iloprost or saline. In the long-term treatment experiment, 18 mice were exposed to LPS/elastase and then received 6 wk of iloprost or were left untreated as controls. In the short-term experiment, iloprost did not change AHR but significantly reduced serum IL-5 and IFN-γ. Long-term treatment with iloprost for both 2 and 6 wk significantly improved AHR. After 6 wk of iloprost, there was a reduction in bronchoalveolar lavage (BALF) neutrophils, serum IL-1β (30.0 ± 9.2 vs. 64.8 ± 7.4 pg/ml, P = 0.045), IL-2 (36.5 ± 10.6 vs. 83.8 ± 0.4 pg/ml, P = 0.01), IL-10 (75.7 ± 9.3 vs. 96.5 ± 3.5 pg/ml, P = 0.02), and nitrite (15.1 ± 5.4 vs. 30.5 ± 10.7 μmol, P = 0.01). Smooth muscle actin (SMA) in the lung homogenate was also significantly reduced after iloprost treatment (P = 0.02), and SMA thickness was reduced in the small and medium blood vessels after iloprost (P < 0.001). In summary, short- and long-term treatment with intranasal iloprost significantly reduced systemic inflammation in an LPS/elastase COPD model. Long-term iloprost treatment also reduced AHR, serum nitrite, SMA, and BALF neutrophilia. These data encourage future investigations of prostanoid therapy as a novel treatment for COPD patients.

PARP inhibition by olaparib or gene knockout blocks asthma-like manifestation in mice by modulating CD4(+) T cell function

Background

An important portion of asthmatics do not respond to current therapies. Thus, the need for new therapeutic drugs is urgent. We have demonstrated a critical role for PARP in experimental asthma. Olaparib, a PARP inhibitor, was recently introduced in clinical trials against cancer. The objective of the present study was to examine the efficacy of olaparib in blocking established allergic airway inflammation and hyperresponsiveness similar to those observed in human asthma in animal models of the disease.

Methods

We used ovalbumin (OVA)-based mouse models of asthma and primary CD4⁺ T cells. C57BL/6J WT or PARP-1^−/− mice were subjected to OVA sensitization followed by a single or multiple challenges to aerosolized OVA or left unchallenged. WT mice were administered, i.p., 1 mg/kg, 5 or 10 mg/kg of olaparib or saline 30 min after each OVA challenge.

Results

Administration of olaparib in mice 30 min post-challenge promoted a robust reduction in airway eosinophilia, mucus production and hyperresponsiveness even after repeated challenges with ovalbumin. The protective effects of olaparib were linked to a suppression of Th2 cytokines eotaxin, IL-4, IL-5, IL-6, IL-13, and M-CSF, and ovalbumin-specific IgE with an increase in the Th1 cytokine IFN-γ. These traits were associated with a decrease in splenic CD4⁺ T cells and concomitant increase in T-regulatory cells. The aforementioned traits conferred by olaparib administration were consistent with those observed in OVA-challenged PARP-1^−/− mice. Adoptive transfer of Th2-skewed OT-II-WT CD4⁺ T cells reversed the Th2 cytokines IL-4, IL-5, and IL-10, the chemokine GM-CSF, the Th1 cytokines IL-2 and IFN-γ, and ovalbumin-specific IgE production in ovalbumin-challenged PARP-1^−/−mice suggesting a role for PARP-1 in CD4⁺ T but not B cells. In ex vivo studies, PARP inhibition by olaparib or PARP-1 gene knockout markedly reduced CD3/CD28-stimulated gata-3 and il4 expression in Th2-skewed CD4⁺ T cells while causing a moderate elevation in t-bet and ifn-γ expression in Th1-skewed CD4⁺ T cells.

Conclusions

Our findings show the potential of PARP inhibition as a viable therapeutic strategy and olaparib as a likely candidate to be tested in human asthma clinical trials.

DNA-dependent protein kinase plays a role in inflammation independent of DNA-damage repair function and its inhibition blocks allergic inflammation in mice and modulates human CD4+ T cell function without causing SCID (HYP7P.264)

We reported that DNA- dependent protein kinase (DNA-PK) is critical for the expression of NF-κB-dependent genes in TNF-α -treated glioblastoma cells including VCAM-1. Here we show that DNA-PK protein level and function are critical for VCAM-1 expression in TNF-α-treated human endothelial and mouse lung smooth muscle cells and are required for monocytes adhesion. Interestingly, DNA-PK activation and subsequent VCAM-1 expression in presence of TNF occurred independently of DNA breaks/repair. Administration of the DNA-PK inhibitor, NU7441, and DNA-PK heterozygosity reduced airway eosinophilia, mucus hypersecretion, airway hyperresponsiveness (AHR), and OVA-specific IgE production in asthma model of mice. Such effects correlated with a marked reduction in lung VCAM-1 expression and production of several inflammatory cytokines. Remarkably, such protection occurred without causing SCID. These results were confirmed in a chronic model of asthma using house dust mite. DNA-PK inhibition reduced Th2 cytokines production without affecting Th1 cytokines production and cell proliferation in CD3/CD28-stimulated human CD4+T cells potentially by blocking gata-3 expression. In mouse CD4+T cells, DNA-PK inhibition, in vitro, severely blocked CD3/CD28-induced gata-3 and t-bet expression and prevented differentiation of Th1 and Th2 cells. Thus, our results suggest DNA-PK as a novel determinant of asthma and a potential target for the treatment of the disease.

PARP inhibition by olaparib or gene knockout blocks asthma manifestation in mice by modulating CD4+ T cell function (HYP2P.324)

An important portion of asthmatics do not respond to current therapies. Thus, the need for new therapeutic drugs becomes urgent. We have demonstrated a critical role for PARP in experimental asthma. In the current study, we test the efficacy of Olaparib, a PARP inhibitor, recently introduced in clinical trials against cancer in blocking established asthma traits in animal models of the disease and determine the mechanism by which it achieves such protection. We show that administration of olaparib in mice post-challenge conferred a robust reduction in airway eosinophilia, mucus production and hyperresponsiveness even after repeated challenges with ovalbumin. The protective effects of olaparib were linked to a suppression of Th2 cytokines and ova-specific IgE with an increase in the Th1 cytokine IFN-g. These traits were associated with a decrease in splenic CD4+T cells and concomitant increase in T-regulatory cells. Adoptive transfer of Th2-skewed OT-II-WT CD4+T cells reversed both Th2 and Th1 cytokines and ova-specific IgE production in ovalbumin-challenged naïve PARP-1-/- mice suggesting a role for PARP-1 in CD4+T but not B cells. Our ex vivo studies show that olaparib treatment markedly reduced CD3/CD28-stimulated gata-3 and il4 expression in Th2-skewed CD4+T cells while causing an elevation in t-bet and ifn-g expression in Th1-skewed CD4+T cells. Our findings show the potential of PARP inhibition as a viable therapeutic strategy to be tested in human clinical trials

PARP inhibition blocks chronic asthma symptoms in a house dust mite asthma model and differentially modulates human CD4+T cell function (HYP2P.332)

Asthma incidence is on the rise. In the United States alone, more than 20 million individuals suffer from the disease. A sizable portion of these asthmatics do not respond to the existing drugs. Accordingly, the need for new therapies is an immediate a necessity. One of the most essential goals for treatment is the identification of drugs that block the release or effects of Th2 cytokines. Using HDM-based chronic model, we show that a single administration of olaparib, a PARP inhibitor, was effective in decreasing lung eosinophilia. Two additional administrations of the drug provided better protection and significantly reduced airway hyper-responsiveness. These results were confirmed using similarly exposed PARP-1−/− mice. Such protective effects may be mediated by a significant reduction in Th2 cytokines and a concomitant increase in T-regulatory cells. In addition, we show that PARP is highly activated in lung tissues and PBMCs from asthmatics demonstrating the relevance to the human disease. Using human CD4+T cells, we show that PARP inhibition significantly reduced GATA-3 expression, Th2 cytokine production without affecting production of IFN-γ, T cell proliferation, or the overall numbers of Th1 or Th2 cells. However and similarly to our animal studies, PARP inhibition markedly increased the number of human T-regulatory cells. Our results provide an additional support to the potential of PARP inhibition as a novel strategy for the treatment of asthma

Inhibition of fatty acid oxidation blocks asthma in mice (HYP2P.340)

Background: There has been a growing appreciation for the role of energy metabolic pathways in the differentiation and function of immune cells. Unpublished findings from our laboratory suggest that inhibiting fatty acid oxidation (FAO) modulates the activation and function of tumor-infiltrating myeloid cells, indicating a potentially important role for FAO in inflammation and thus inflammatory diseases such as asthma. Objective: We sought to test the hypothesis that FAO plays an important role in asthma manifestation. Methods: Etomoxir, an inhibitor of the FAO rate-limiting enzyme carnithine palmitoyltransferase-1, was used to test our hypothesis in an ovalbumin-based murine model of asthma. Results: Etomoxir treatment thirty minutes after ovalbumin challenge resulted in a significant reduction in the recruitment of eosinophils and macrophages into the lungs without a prominent effect on the total number of lymphocytes. Etomoxir treatment also prevented ovalbumin-induced hyperresponsiveness. The protective effects of etomoxir were associated with a decrease in Th2 cytokines and ovalbumin-specific IgE production. Additionally, the frequency of splenic macrophages was lower in etomoxir-treated mice, compared with control. Conclusions: Our preliminary data suggest the inhibition of FAO as a likely strategy to block asthma traits. As such, we are currently uncovering the mechanisms by which FAO inhibition reduces the pathogenesis of asthma.

Common and differential roles of inducible NO synthase and poly (ADP-ribose)polymerase in allergen-induced inflammation and airway hyperresponsiveness: a potential connection to NO levels (HYP5P.320)

The potential role of iNOS as a viable therapeutic target for the treatment of asthma was severely hampered by the negative clinical trial results showing that a selective iNOS inhibitor did not affect airway hyperreactivity (AHR) or airway inflammation after allergen challenge in human subjects with asthma. Our laboratory has shown that iNOS inhibition is protective against airway inflammation upon acute, but not chronic, exposures to ovalbumin. More importantly, iNOS inhibition protected against lung fibrosis suggesting that iNOS inhibition may be protective against some aspects of asthma. Here, we show that iNOS inhibition, pharmacologically by L-Nil or by gene knockout, provided an excellent protection against AHR upon an acute, but not chronic, exposure to ovalbumin. Our laboratory also established a reciprocal relationship between iNOS and PARP-1. However, PARP inhibition, protected against inflammation and AHR upon acute and chronic exposure to ovalbumin. It is interesting that PARP-1 inhibition does not completely abrogate expression of iNOS leaving the possibility that the protective effect of PARP inhibition against inflammation and AHR may be associated with reduction but not the complete inhibition of iNOS and associated production of moderate levels of NO. Studies are being conducted to verify this hypothesis and clarify the intricate roles of iNOS in asthma pathogenesis allowing the possibility of being a viable target for the treatment of the disease.

DNA-dependent protein kinase inhibition blocks asthma in mice and modulates human endothelial and CD4⁺ T-cell function without causing severe combined immunodeficiency

BACKGROUND

We reported that DNA-dependent protein kinase (DNA-PK) is critical for the expression of nuclear factor κB-dependent genes in TNF-α-treated glioblastoma cells, suggesting an involvement in inflammatory diseases.

OBJECTIVE

We sought to investigate the role of DNA-PK in asthma.

METHODS

Cell culture and ovalbumin (OVA)- or house dust mite-based murine asthma models were used in this study.

RESULTS

DNA-PK was essential for monocyte adhesion to TNF-α-treated endothelial cells. Administration of the DNA-PK inhibitor NU7441 reduced airway eosinophilia, mucus hypersecretion, airway hyperresponsiveness, and OVA-specific IgE production in mice prechallenged with OVA. Such effects correlated with a marked reduction in lung vascular cell adhesion molecule 1 expression and production of several cytokines, including IL-4, IL-5, IL-13, eotaxin, IL-2, and IL-12 and the chemokines monocyte chemoattractant protein 1 and keratinocyte-derived chemokine, with a negligible effect on IL-10/IFN-γ production. DNA-PK inhibition by gene heterozygosity of the 450-kDa catalytic subunit of the kinase (DNA-PKcs(+/-)) also prevented manifestation of asthma-like traits. These results were confirmed in a chronic model of asthma by using house dust mite, a human allergen. Remarkably, such protection occurred without causing severe combined immunodeficiency. Adoptive transfer of TH2-skewed OT-II wild-type CD4(+) T cells reversed IgE and TH2 cytokine production but not airway hyperresponsiveness in OVA-challenged DNA-PKcs(+/-) mice. DNA-PK inhibition reduced IL-4, IL-5, IL-13, eotaxin, IL-8, and monocyte chemoattractant protein 1 production without affecting IL-2, IL-12, IFN-γ, and interferon-inducible protein 10 production in CD3/CD28-stimulated human CD4(+) T cells, potentially by blocking expression of Gata3. These effects occurred without significant reductions in T-cell proliferation. In mouse CD4(+) T cells in vitro DNA-PK inhibition severely blocked CD3/CD28-induced Gata3 and T-bet expression in CD4(+) T cells and prevented differentiation of TH1 and TH2 cells under respective TH1- and TH2-skewing conditions.

CONCLUSION

Our results suggest DNA-PK as a novel determinant of asthma and a potential target for the treatment of the disease.

Effects of intrathecal fentanyl as an adjunct to hyperbaric bupivacaine in spinal anesthesia for elective caesarean section

Hyperbaric bupivacaine is the most common drug used in spinal anesthesia for caesarean section. The aim of this study was to compare the effects of adding fentanyl to intrathecal bupivacaine on the onset and duration of spinal anesthesia and its effect on mother and neonate. Seventy healthy parturients with singleton pregnancy scheduled for elective cesarean section were randomly allocated to receive subarachnoid block with 0.5% bupivacaine heavy 2.4 ml (Group A) or fentanyl 20 microgram (0.4 ml) added to 0.5% bupivacaine heavy 2 ml (Group B). Blood pressure, heart rate, respiratory rate, oxygen saturation, along with characteristics of spinal block were assessed throughout the surgery and in the postoperative ward until the patient requested for analgesia. It was found that duration of sensory block was prolonged in fentanyl group (p < 0.05). Duration of complete analgesia (97 ± 8.23 minutes vs 153 ± 7 minutes; p value = 0.00) and effective analgesia (134 ± 5.6 minutes vs 164 ± 9; p value = 0.00) were also found to be prolonged in Group B. There was not much difference in the occurrence of side effects in both the groups. Addition of fentanyl to intrathecal bupivacaine for cesarean section increases the duration of postoperative analgesia without increasing maternal or neonatal side effects.

Minocycline blocks asthma-associated inflammation in part by interfering with the T cell receptor-nuclear factor κB-GATA-3-IL-4 axis without a prominent effect on poly(ADP-ribose) polymerase

Minocycline protects against asthma independently of its antibiotic function and was recently reported as a potent poly(ADP-ribose) polymerase (PARP) inhibitor. In an animal model of asthma, a single administration of minocycline conferred excellent protection against ovalbumin-induced airway eosinophilia, mucus hypersecretion, and Th2 cytokine production (IL-4/IL-5/IL-12(p70)/IL-13/GM-CSF) and a partial protection against airway hyperresponsiveness. These effects correlated with pronounced reduction in lung and sera allergen-specific IgE. A reduction in poly(ADP-ribose) immunoreactivity in the lungs of minocycline-treated/ovalbumin-challenged mice correlated with decreased oxidative DNA damage. The effect of minocycline on PARP may be indirect, as the drug failed to efficiently block direct PARP activation in lungs of N-methyl-N'-nitro-N-nitroso-guanidine-treated mice or H(2)O(2)-treated cells. Minocycline blocked allergen-specific IgE production in B cells potentially by modulating T cell receptor (TCR)-linked IL-4 production at the mRNA level but not through a modulation of the IL-4-JAK-STAT-6 axis, IL-2 production, or NFAT1 activation. Restoration of IL-4, ex vivo, rescued IgE production by minocycline-treated/ovalbumin-stimulated B cells. IL-4 blockade correlated with a preferential inhibition of the NF-κB activation arm of TCR but not GSK3, Src, p38 MAPK, or ERK1/2. Interestingly, the drug promoted a slightly higher Src and ERK1/2 phosphorylation. Inhibition of NF-κB was linked to a complete blockade of TCR-stimulated GATA-3 expression, a pivotal transcription factor for IL-4 expression. Minocycline also reduced TNF-α-mediated NF-κB activation and expression of dependent genes. These results show a potentially broad effect of minocycline but that it may block IgE production in part by modulating TCR function, particularly by inhibiting the signaling pathway, leading to NF-κB activation, GATA-3 expression, and subsequent IL-4 production.