Andrew J. Rasky

Marine algal toxin azaspiracid is an open-state blocker of hERG potassium channels.

Azaspiracids (AZA) are polyether marine dinoflagellate toxins that accumulate in shellfish and represent an emerging human health risk. Although human exposure is primarily manifested by severe and protracted diarrhea, this toxin class has been shown to be highly cytotoxic, a teratogen to developing fish, and a possible carcinogen in mice. Until now, AZAs molecular target has not yet been determined. Using three independent methods (voltage clamp, channel binding assay, and thallium flux assay), we have for the first time demonstrated that AZA1, AZA2, and AZA3 each bind to and block the hERG (human ether-à-go-go related gene) potassium channel heterologously expressed in HEK-293 mammalian cells. Inhibition of K(+) current for each AZA analogue was concentration-dependent (IC(50) value range: 0.64-0.84 μM). The mechanism of hERG channel inhibition by AZA1 was investigated further in Xenopus oocytes where it was shown to be an open-state-dependent blocker and, using mutant channels, to interact with F656 but not with Y652 within the S6 transmembrane domain that forms the channels central pore. AZA1, AZA2, and AZA3 were each shown to inhibit [(3)H]dofetilide binding to the hERG channel and thallium ion flux through the channel (IC(50) value range: 2.1-6.6 μM). AZA1 did not block the K(+) current of the closely related EAG1 channel. Collectively, these data suggest that the AZAs physically block the K(+) conductance pathway of hERG1 channels by occluding the cytoplasmic mouth of the open pore. Although the concentrations necessary to block hERG channels are relatively high, AZA-induced blockage may prove to contribute to the toxicological properties of the AZAs.

Sirtuin 1 regulates dendritic cell activation and autophagy during respiratory syncytial virus-induced immune responses

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in children worldwide. Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, has been associated with the induction of autophagy and the regulation of inflammatory mediators. We found that Sirt1 was upregulated in mouse lung after RSV infection. Infected animals that received EX-527, a selective SIRT1 inhibitor, displayed exacerbated lung pathology, with increased mucus production, elevated viral load, and enhanced Th2 cytokine production. Gene expression analysis of isolated cell populations revealed that Sirt1 was most highly upregulated in RSV-treated dendritic cells (DCs). Upon RSV infection, EX-527–treated DCs, Sirt1 small interfering RNA–treated DCs, or DCs from conditional knockout (Sirt1f/f-CD11c-Cre+) mice showed downregulated inflammatory cytokine gene expression and attenuated autophagy. Finally, RSV infection of Sirt1f/f-CD11c-Cre+ mice resulted in altered lung and lymph node cytokine responses, leading to exacerbated pathology. These data indicate that SIRT1 promotes DC activation associated with autophagy-mediated processes during RSV infection, thereby directing efficient antiviral immune responses.

IL-17E (IL-25) and IL-17RB promote respiratory syncytial virus-induced pulmonary disease

One of the most severe pathologic responses of RSV infection is associated with overproduction of cytokines and inflammation, leading to mucus hypersecretion. This study investigated the role of IL‐25 in the development of RSV‐associated immunopathology. IL‐25 and its receptor IL‐17RB were increased following RSV infection, and IL‐25 blockade using neutralizing antibodies reduced RSV‐associated pathology, AHR, and type 2 cytokine production. Likewise, IL‐17RB−/− mice demonstrated a modified inflammatory response during RSV infection characterized by decreased Th2 and increased Th17 cytokine production. Additionally, the IL‐17RB−/− mice demonstrated significantly reduced inflammation and cytokine production in a model of RSV‐driven asthma exacerbation. These results indicate that IL‐25 regulates the inflammatory response to RSV infection and that its inhibition may enable a reduction in the severity of RSV‐associated pulmonary inflammation, including during viral‐induced asthma exacerbation.

STAT5-Induced Lunatic Fringe during Th2 Development Alters Delta-like 4–Mediated Th2 Cytokine Production in Respiratory Syncytial Virus–Exacerbated Airway Allergic Disease

Notch activation plays an important role in T cell development and mature T cell differentiation. In this study, we investigated the role of Notch activation in a mouse model of respiratory syncytial virus (RSV)–exacerbated allergic airway disease. During RSV exacerbation, in vivo neutralization of a specific Notch ligand, Delta-like ligand (Dll)-4, significantly decreased airway hyperreactivity, mucus production, and Th2 cytokines. Lunatic Fringe (Lfng), a glycosyltransferase that enhances Notch activation by Dll4, was increased during RSV exacerbation. Lfng loss of function in Th2-skewed cells inhibited Dll4-Notch activation and subsequent IL-4 production. Further knockdown of Lfng in T cells in CD4Cre+Lfngfl/fl mice showed reduced Th2 response and disease pathology during RSV exacerbation. Finally, we identified STAT5-binding cis-acting regulatory element activation as a critical driver of Lfng transcriptional activation. These data demonstrate that STAT5-dependent amplification of Notch-modifying Lfng augments Th2 response via Dll4 and is critical for amplifying viral exacerbation during allergic airway disease.

Lactobacillus johnsonii supplementation attenuates respiratory viral infection via metabolic reprogramming and immune cell modulation

Regulation of respiratory mucosal immunity by microbial-derived metabolites has been a proposed mechanism that may provide airway protection. Here we examine the effect of oral Lactobacillus johnsonii supplementation on metabolic and immune response dynamics during respiratory syncytial virus (RSV) infection. L. johnsonii supplementation reduced airway T helper type 2 cytokines and dendritic cell (DC) function, increased regulatory T cells, and was associated with a reprogrammed circulating metabolic environment, including docosahexanoic acid (DHA) enrichment. RSV-infected bone marrow–derived DCs (BMDCs) from L. johnsonii–supplemented mice had altered cytokine secretion, reduced expression of co-stimulatory molecules, and modified CD4+ T-cell cytokines. This was replicated upon co-incubation of wild-type BMDCs with either plasma from L. johnsonii–supplemented mice or DHA. Finally, airway transfer of BMDCs from L. johnsonii–supplemented mice or with wild-type derived BMDCs pretreated with plasma from L. johnsonii–supplemented mice reduced airway pathological responses to infection in recipient animals. Thus L. johnsonii supplementation mediates airway mucosal protection via immunomodulatory metabolites and altered immune function.

Notch Ligand Delta-like 4 Promotes Regulatory T Cell Identity in Pulmonary Viral Infection

Regulatory T (Treg) cells establish tolerance, prevent inflammation at mucosal surfaces, and regulate immunopathology during infectious responses. Recent studies have shown that Delta-like ligand 4 (Dll4) was upregulated on APC after respiratory syncytial virus (RSV) infection, and its inhibition leads to exaggerated immunopathology. In the present study, we outline the role of Dll4 in Treg cell differentiation, stability, and function in RSV infection. We found that Dll4 was expressed on CD11b+ pulmonary dendritic cells in the lung and draining lymph nodes in wild-type BALB/c mice after RSV infection. Dll4 neutralization exacerbated RSV-induced disease pathology, mucus production, group 2 innate lymphoid cell infiltration, IL-5 and IL-13 production, as well as IL-17A+ CD4 T cells. Dll4 inhibition decreased the abundance of CD62LhiCD44loFoxp3+ central Treg cells in draining lymph nodes. The RSV-induced disease was accompanied by an increase in Th17-like effector phenotype in Foxp3+ Treg cells and a decrease in granzyme B expression after Dll4 blockade. Finally, Dll4-exposed induced Treg cells maintained the CD62LhiCD44lo central Treg cell phenotype, had increased Foxp3 expression, became more suppressive, and were resistant to Th17 skewing in vitro. These results suggest that Dll4 activation during differentiation sustained Treg cell phenotype and function to control RSV infection.

Loss of Hox5 function results in myofibroblast mislocalization and distal lung matrix defects during postnatal development

Alveologenesis is the final stage of lung development and is responsible for the formation of the principle gas exchange units called alveoli. The lung mesenchyme, in particular the alveolar myofibroblasts, are drivers of alveolar development, however, few key regulators that govern the proper distribution and behavior of these cells in the distal lung during alveologenesis have been identified. While Hox5 triple mutants (Hox5 aabbcc) exhibit neonatal lethality, four-allele, compound mutant mice (Hox5 AabbCc) are born in Mendelian ratios and are phenotypically normal at birth. However, they exhibit defects in alveologenesis characterized by a BPD-like phenotype by early postnatal stages that becomes more pronounced at adult stages. Invasive pulmonary functional analyses demonstrate significant increases in total lung volume and compliance and a decrease in elastance in Hox5 compound mutants. SMA+ myofibroblasts in the distal lung are distributed abnormally during peak stages of alveologenesis and aggregate, resulting in the formation of a disrupted elastin network. Examination of other key components of the distal lung ECM, as well as other epithelial cells and lipofibroblasts reveal no differences in distribution. Collectively, these data indicate that Hox5 genes play a critical role in alveolar development by governing the proper cellular behavior of myofibroblasts during alveologenesis.

Hox5 genes direct elastin network formation during alveologenesis by regulating myofibroblast adhesion

Significance Hox5 genes play critical roles in embryonic lung development, but mutants die at birth, preventing investigation of potential postnatal functions for these genes. Surprisingly, we show that the highest expression levels of Hox5 genes occur 1–2 weeks after birth. We created a conditional allele for Hoxa5 that allowed us to generate and study mutants for all three Hox5 genes during postnatal development. Hox5 mutants have poorly developed alveoli and expanded distal airspaces resulting from an abrogated elastin network. These defects arise from the inability of Hox5 mutant fibroblasts to adhere to the fibronectin matrix due to loss of integrins Itga5/b1. Thus, our data highlight redundant roles for all three Hox5 genes in regulating fibroblast adhesion and elastogenesis during alveologenesis. Hox5 genes (Hoxa5, Hoxb5, Hoxc5) are exclusively expressed in the lung mesenchyme during embryogenesis, and the most severe phenotypes result from constitutive loss of function of all three genes. Because Hox5 triple null mutants exhibit perinatal lethality, the contribution of this paralogous group to postembryonic lung development is unknown. Intriguingly, expression of all three Hox5 genes peaks during the first 2 weeks after birth, reaching levels far exceeding those measured at embryonic stages, and surviving Hoxa5 single and Hox5 AabbCc compound mutants exhibit defects in the localization of alveolar myofibroblasts. To define the contribution of the entire Hox5 paralogous group to this process, we generated an Hoxa5 conditional allele to use with our existing null alleles for Hoxb5 and Hoxc5. Postnatally, mesenchymal deletion of Hoxa5 in an Hoxb5/Hoxc5 double-mutant background results in severe alveolar simplification. The elastin network required for alveolar formation is dramatically disrupted in Hox5 triple mutants, while the basal lamina, interstitial matrix, and fibronectin are normal. Alveolar myofibroblasts remain Pdgfrα+/SMA+ double positive and present in normal numbers, indicating that the irregular elastin network is not due to fibroblast differentiation defects. Rather, we observe that SMA+ myofibroblasts of Hox5 triple mutants are morphologically abnormal both in vivo and in vitro with highly reduced adherence to fibronectin. This loss of adhesion is a result of loss of the integrin heterodimer Itga5b1 in mutant fibroblasts. Collectively, these data show an important role for Hox5 genes in lung fibroblast adhesion necessary for proper elastin network formation during alveologenesis.

Notch ligand Delta-like 4 induces epigenetic regulation of Treg cell differentiation and function in viral infection

Notch ligand Delta-like ligand 4 (DLL4) has been shown to regulate CD4 T-cell differentiation, including regulatory T cells (Treg). Epigenetic alterations, which include histone modifications, are critical in cell differentiation decisions. Recent genome-wide studies demonstrated that Treg have increased trimethylation on histone H3 at lysine 4 (H3K4me3) around the Treg master transcription factor, Foxp3 loci. Here we report that DLL4 dynamically increased H3K4 methylation around the Foxp3 locus that was dependent upon upregulated SET and MYDN domain containing protein 3 (SMYD3). DLL4 promoted Smyd3 through the canonical Notch pathway in iTreg differentiation. DLL4 inhibition during pulmonary respiratory syncytial virus (RSV) infection decreased Smyd3 expression and Foxp3 expression in Treg leading to increased Il17a. On the other hand, DLL4 supported Il10 expression in vitro and in vivo, which was also partially dependent upon SMYD3. Using genome-wide unbiased mRNA sequencing, novel sets of DLL4- and Smyd3-dependent differentially expressed genes were discovered, including lymphocyte-activation gene 3 (Lag3), a checkpoint inhibitor that has been identified for modulating Th cell activation. Together, our data demonstrate a novel mechanism of DLL4/Notch-induced Smyd3 epigenetic pathways that maintain regulatory CD4 T cells in viral infections.