Sensitive genetically encoded sensors for population and subcellular imaging of cAMP in vivo.

Cyclic adenosine monophosphate (cAMP) signaling integrates information from diverse G-protein-coupled receptors, such as neuromodulator receptors, to regulate pivotal biological processes in a cellular-specific and subcellular-specific manner. However, in vivo cellular-resolution imaging of cAMP dynamics remains challenging. Here, we screen existing genetically encoded cAMP sensors and further develop the best performer to derive three improved variants, called cAMPFIREs. Compared with their parental sensor, these sensors exhibit up to 10-fold increased sensitivity to cAMP and a cytosolic distribution. cAMPFIREs are compatible with both ratiometric and fluorescence lifetime imaging and can detect cAMP dynamics elicited by norepinephrine at physiologically relevant, nanomolar concentrations. Imaging of cAMPFIREs in awake mice reveals tonic levels of cAMP in cortical neurons that are associated with wakefulness, modulated by opioids, and differentially regulated across subcellular compartments. Furthermore, enforced locomotion elicits neuron-specific, bidirectional cAMP dynamics. cAMPFIREs also function in Drosophila. Overall, cAMPFIREs may have broad applicability for studying intracellular signaling in vivo.

Molecular principles of assembly, activation, and inhibition in epithelial sodium channel.

The molecular bases of heteromeric assembly and link between Na+ self-inhibition and protease-sensitivity in epithelial sodium channels (ENaCs) are not fully understood. Previously, we demonstrated that ENaC subunits - α, ß, and γ - assemble in a counterclockwise configuration when viewed from outside the cell with the protease-sensitive GRIP domains in the periphery (Noreng et al., 2018). Here we describe the structure of ENaC resolved by cryo-electron microscopy at 3 Å. We find that a combination of precise domain arrangement and complementary hydrogen bonding network defines the subunit arrangement. Furthermore, we determined that the α subunit has a primary functional module consisting of the finger and GRIP domains. The module is bifurcated by the α2 helix dividing two distinct regulatory sites: Na+ and the inhibitory peptide. Removal of the inhibitory peptide perturbs the Na+ site via the α2 helix highlighting the critical role of the α2 helix in regulating ENaC function.

Structure of the human epithelial sodium channel by cryo-electron microscopy.

The epithelial sodium channel (ENaC), a member of the ENaC/DEG superfamily, regulates Na+ and water homeostasis. ENaCs assemble as heterotrimeric channels that harbor protease-sensitive domains critical for gating the channel. Here, we present the structure of human ENaC in the uncleaved state determined by single-particle cryo-electron microscopy. The ion channel is composed of a large extracellular domain and a narrow transmembrane domain. The structure reveals that ENaC assembles with a 1:1:1 stoichiometry of α:ß:γ subunits arranged in a counter-clockwise manner. The shape of each subunit is reminiscent of a hand with key gating domains of a 'finger' and a 'thumb.' Wedged between these domains is the elusive protease-sensitive inhibitory domain poised to regulate conformational changes of the 'finger' and 'thumb'; thus, the structure provides the first view of the architecture of inhibition of ENaC.

Molecular Signals Involved in Human B Cell Migration into the Retina: In Vitro Investigation of ICAM-1, VCAM-1, and CXCL13.

PURPOSE: B cells participate in diverse retinal immunopathologies. Endothelial adhesion molecules and chemokines direct leukocyte trafficking. We examined the involvement of three molecular signals in retinal transendothelial migration of human B cells: ICAM-1, VCAM-1, and CXCL13. METHODS: Peripheral blood B cells were isolated by negative selection. Migration was studied in transwells populated with human retinal endothelial monolayers, using antibody to block ICAM-1 or VCAM-1. Retinal expression of CXCL13 was investigated. RESULTS: B cells crossed retinal endothelium. ICAM-1 blockade significantly reduced migration when results for all subjects were combined, and for a majority when results were analyzed by individual. This effect was irrespective of the presence or absence of CXCL13, although CXCL13 increased migration. CXCL13 was detected in neural retina and retinal pigment epithelium. Endothelial cells of some retinal vessels presented CXCL13 protein. CONCLUSION: ICAM-1 blockade may be an effective treatment in some patients with retinal diseases that involve B cells.

Involvement of B cells in non-infectious uveitis.

Non-infectious uveitis-or intraocular inflammatory disease-causes substantial visual morbidity and reduced quality of life amongst affected individuals. To date, research of pathogenic mechanisms has largely been focused on processes involving T lymphocyte and/or myeloid leukocyte populations. Involvement of B lymphocytes has received relatively little attention. In contrast, B-cell pathobiology is a major field within general immunological research, and large clinical trials have showed that treatments targeting B cells are highly effective for multiple systemic inflammatory diseases. B cells, including the terminally differentiated plasma cell that produces antibody, are found in the human eye in different forms of non-infectious uveitis; in some cases, these cells outnumber other leukocyte subsets. Recent case reports and small case series suggest that B-cell blockade may be therapeutic for patients with non-infectious uveitis. As well as secretion of antibody, B cells may promote intraocular inflammation by presentation of antigen to T cells, production of multiple inflammatory cytokines and support of T-cell survival. B cells may also perform various immunomodulatory activities within the eye. This translational review summarizes the evidence for B-cell involvement in non-infectious uveitis, and considers the potential contributions of B cells to the development and control of the disease. Manipulations of B cells and/or their products are promising new approaches to the treatment of non-infectious uveitis.

Intercellular adhesion molecule 1 mediates migration of Th1 and Th17 cells across human retinal vascular endothelium.

PURPOSE: Autoimmune inflammation of the retina causes vision loss in the majority of affected individuals. Th1 or Th17 cells initiate the disease on trafficking from the circulation into the eye across the retinal vascular endothelium. We investigated the ability of human Th1- and Th17-polarized cells to cross a simulated human retinal endothelium, and examined the role of IgG superfamily members in this process. METHODS: Th1- and Th17-polarized cell populations were generated from human peripheral blood CD4(+) T cells, using two Th1- and Th17-polarizing protocols. Transendothelial migration assays were performed over 18 hours in Boyden chambers, after seeding the transwell membrane with human retinal endothelial cells. In some assays intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), or activated leukocyte cell adhesion molecule (ALCAM) blocking antibody, or isotype- and concentration-matched control antibody, was added to the upper chambers. RESULTS: Th1- and Th17-polarized cells migrated equally efficiently across the human retinal endothelial monolayer. The percentage of IL-17(+) IFN-γ(-) Th17-polarized cells was reduced following migration. Blocking ICAM-1, but not VCAM-1 or ALCAM, significantly reduced migration of Th1- and Th17-polarized cells for a majority of human donors. CONCLUSIONS: Taken in the context of other literature on transendothelial migration, our results illustrate the importance of investigating the specific tissue and vascular endothelium when considering helper T cell migration in autoimmune inflammation. Our findings further indicate that while generalizations about involvement of specific adhesion molecules in uveitis and other autoimmune disease may be possible, these may not apply to individual patients universally. The observations are relevant to the use of adhesion blockade for therapeutic purposes.

Role of the retinal vascular endothelial cell in ocular disease.

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

Migration of toxoplasma gondii-infected dendritic cells across human retinal vascular endothelium.

PURPOSE: Toxoplasma gondii, the parasite responsible for ocular toxoplasmosis, accesses the retina from the bloodstream. We investigated the dendritic cell as a potential taxi for T. gondii tachyzoites moving across the human retinal endothelium, and examined the participation of adhesion molecules and chemokines in this process. METHODS: CD14-positive monocytes were isolated from human peripheral blood by antibody-mediated cell enrichment, and cultured in granulocyte-macrophage colony-stimulating factor and interleukin-4 to generate dendritic cells. Transmigration assays were performed over 18 hours in transwells seeded with human retinal endothelial cells and using dendritic cells exposed to laboratory or natural strains of T. gondii tachyzoites. Parasites were tagged with yellow fluorescent protein to verify infection. In some experiments, endothelial monolayers were preincubated with antibody directed against adhesion molecules, or chemokine was added to lower chambers of transwells. RESULTS: Human monocyte-derived dendritic cell preparations infected with laboratory or natural strain T. gondii tachyzoites transmigrated in larger numbers across simulated human retinal endothelium than uninfected dendritic cells (P ≤ 0.0004 in 5 of 6 experiments). Antibody blockade of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and activated leukocyte cell adhesion molecule (ALCAM) inhibited transmigration (P ≤ 0.007), and CCL21 or CXCL10 increased transmigration (P ≤ 0.031). CONCLUSIONS: Transmigration of human dendritic cells across retinal endothelium is increased following infection with T. gondii. Movement may be impacted by locally produced chemokines and is mediated in part by ICAM-1, VCAM-1, and ALCAM. These findings have implications for development of novel therapeutics aimed at preventing retinal infection by T. gondii.

Toxoplasma gondii tachyzoites cross retinal endothelium assisted by intercellular adhesion molecule-1 in vitro.

Retinal infection is the most common clinical manifestation of toxoplasmosis. The route by which circulating Toxoplasma gondii tachyzoites cross the vascular endothelium to enter the human retina is unknown. Convincing studies using murine encephalitis models have strongly implicated leukocyte taxis as one pathway used by the parasite to access target organs. To establish whether tachyzoites might also interact directly with vascular endothelium, we populated a transwell system with human ocular endothelial cells. Human retinal endothelial monolayers permitted transmigration of tachyzoites of RH and three natural isolate strains. Antibody blockade of intercellular adhesion molecule-1 significantly reduced this migration, but did not impact tachyzoite movement across an endothelial monolayer derived from the choroid, which lies adjacent to the retina within the eye. In demonstrating that tachyzoites are capable of independent migration across human vascular endothelium in vitro, this study carries implications for the development of therapeutics aimed at preventing access of T. gondii to the retina.

Induction of immune tolerance to FIX by intramuscular AAV gene transfer is independent of the activation status of dendritic cells.

The nature of viral vectors is suggested to be a significant contributor to undesirable immune responses subsequent to gene transfer. Such viral vectors, recognized as danger signals by the host immune system, activate dendritic cells (DCs), causing unwanted antivector and/or transgene product immunity. We recently reported efficient induction of immune tolerance to coagulation factor IX (FIX) by direct intramuscular injection of adeno-associated virus (AAV)-FIX. AAV vectors are nonpathogenic and elicit minimal inflammatory response. We hypothesized that the nonpathogenic nature of AAV plays a critical role in induction of tolerance after AAV gene transfer. We observed inefficient recruitment and activation of DCs subsequent to intramuscular injection of AAV. To further validate our hypothesis, we examined immune responses to FIX after intramuscular injection of AAV with simultaneous activation of DCs. We were able to achieve phenotypic and functional activation of DCs after administration of lipopolysaccharide and anti-CD40 antibody. However, we observed efficient induction of FIX tolerance irrespective of DC activation in mice with different genetic and major histocompatibility complex backgrounds. Furthermore, activation of DCs did not exaggerate the immune response induced after intramuscular injection of AAV serotype 2 vector. Our results demonstrate that induction of FIX tolerance after AAV gene transfer is independent of DC activation status.

Regulatory T cells and immune tolerance to coagulation factor IX in the context of intramuscular AAV1 gene transfer.

Regulatory T cells play a major role in induction and maintenance of immune tolerance and immunological homeostasis. A variety of strategies have been attempted to induce regulatory T cells for control of unwanted, adverse immunity in autoimmune diseases, transplantation as well as gene transfer. We recently reported efficient induction of immune tolerance to coagulation factor IX (FIX) following intramuscular AAV1 gene transfer. In the current study, we performed a systematic and comprehensive examination of the role and function of regulatory T cells in induction and maintenance of FIX tolerance in the context of intramuscular AAV1 gene transfer. We observed no significant upregulation of regulatory T cells in the FIX-tolerant mice. In addition, adoptive transfer of splenocytes from FIX-tolerant mice did not suppress anti-hFIX immunity in recipient mice. Both in vitro and in vivo depletion of regulatory T cells failed to reverse FIX tolerance. These observations revealed that regulatory T cells do not play a significant role in the maintenance/protection of the established FIX tolerance. Our results provide critical insight into the role and function of regulatory T cells in induction and maintenance/protection of immune tolerance in gene transfer, complementing the current paradigm of immune tolerance mechanism.

Fms-like tyrosine kinase 3 ligand increases a lung DC subset with regulatory properties in allergic airway inflammation.

BACKGROUND: Dendritic cell (DC) subsets display different functional roles in regulating immune responses and lead to various outcomes, including T(H)1 versus T(H)2 or regulatory versus immunologic responses. Administration of Fms-like tyrosine kinase 3 (Flt3) ligand prevents and reverses allergic airway inflammation and airway hyperresponsiveness in a mouse model. However, the underlying mechanisms are unclear. OBJECTIVE: We characterized and examined the role of lung DC subsets in the therapeutic effect of Flt3 ligand. METHODS: DCs were isolated from the lungs of ovalbumin (OVA)-sensitized and OVA-challenged mice treated with recombinant human Flt3 ligand. Two populations of CD11c+ cells labeled with fluorochrome-conjugated antibodies were sorted. The ability of the purified cells to stimulate T-cell proliferation and cytokine secretion patterns by different DC subsets was examined. Also, DCs were adoptively transferred in mice to examine their effect on pulmonary function. RESULTS: Two DC populations, CD11c(high)CD11b(low) and CD11c(low)CD11b(high), were identified in the lungs of naive and OVA-sensitized and OVA-challenged mice with and without treatment with Flt3 ligand. The expression levels of CD8alpha, B220, CD19, F4/80, MHC II, CCR7, CD40, programmed death ligand 1, programmed death ligand 2, CD80, and CD86 were distinctly different between the 2 DC populations, which supports the notion that CD11c(high)CD11b(low) and CD11c(low)CD11b(high) DCs potentially have regulatory and immunogenic properties, respectively. Administration of Flt3 ligand increased the DCs with regulatory potential in the lungs of antigen-sensitized mice, and CD11c(high)CD11b(low) DCs acquired a maximum degree of regulatory capacity after Flt3 ligand treatment. CONCLUSION: These data suggest that Flt3 ligand reverses airway hyperresponsiveness by regulating the function of lung DCs in a mouse model of allergic airway inflammation.

Induction of immune tolerance to FIX following muscular AAV gene transfer is AAV-dose/FIX-level dependent.

Direct intramuscular injection (IM) of adeno-associated virus (AAV) has been proven a safe and potentially efficient procedure for gene therapy of many genetic diseases including hemophilia B. It is, however, contentious whether high antigen level induces tolerance or immunity to coagulation factor IX (FIX) following IM of AAV. We recently reported induction of FIX-specific immune tolerance by IM of AAV serotype one (AAV1) vector in mice. We hypothesize that the expression of high levels of FIX is critical to induction of FIX tolerance. In this study, we investigated the correlation among AAV dose, FIX expression, and tolerance induction. We observed that induction of immune tolerance or immunity to FIX was dependent on the dose of AAV1-human FIX (hFIX) given and the level of FIX antigen expressed in both normal and hemophilia mice. We then defined the minimum AAV1-hFIX dose and the lowest level of FIX needed for FIX tolerance. Different from hepatic AAV-hFIX gene transfer, we found that FIX tolerance induced by IM of AAV1 was not driven by regulatory T cells. These results provided further insight into the mechanism(s) of FIX tolerance, contributing to development of hemophilia gene therapy, and optimization of FIX tolerance induction protocols.

Dendritic cells in allergic airway inflammation.

Dendritic cells (DCs) are primary antigen-presenting cells involved in interactions with T cells leading to the proliferation of TH1 or TH2 cell types. In asthma, predominance of TH2 cells appears to be responsible for disease pathogenesis. Differentiation of TH2 cells is driven by a variety of factors such as the expression of high levels of costimulatory molecules, the cytokine profile, and the subset of DCs. Many inflammatory cells involved in the pathogenesis of asthma either directly or indirectly modulate DC function. Traditional treatments for asthma decrease the number of airway DCs in animals as well as in patients with asthma. Immunomodulators including interleukin (IL)-10, transforming growth factor (TGF)-beta, cytosine-phosphate-guanosine-containing oligodeoxynucleotides (CpG-ODN), 1alpha,25-dihydroxyvitamin D3, and fetal liver tyrosine kinase 3 ligand (Flt3L) are involved in the modulation of the function of DCs. Based on the critical review of the interaction between DCs and other inflammatory cells, we propose that activation of T cells by DCs and sensitization to inhaled allergen and resulting airway inflammation are dependent on plasmacytoid and myeloid subset of lung DCs to induce an immune response or tolerance and are tightly regulated by T-regulatory cells. Effects of various therapeutic agents to modulate the function of lung myeloid DCs have been discussed.

Transcription factors in the control of dendritic cell life cycle.

Dendritic cells (DCs) are potent antigen-presenting cells that guard all parts of the body. They have the unique ability to prime T cells and generate primary immune responses. Their journey beginning with the development from precursor cells and ending with their death is controlled by a group of transcription factors. Some of the transcription factors like PU.1 are involved in more than one stage of DC life. Other transcription factors including Ikaros and JAK3 are involved in the development of more than one cell type. For a long time, the cellular and molecular mechanisms underlying the development, differentiation, maturation, and other stages of DC life were not well understood. However, in recent years novel information has been published by many researchers to better understand the molecular mechanisms of the development and function of DCs in immunological diseases such as asthma, cancer, autoimmunity, and transplantation. This review will discuss the various transcription factors and signaling pathways involved in each stage of the life cycle of DCs.

Flt3 ligand generates morphologically distinct semimature dendritic cells in ovalbumin-sensitized mice.

Dendritic cells (DCs) are unique antigen presenting cells that are immature prior to their encounter with an antigen. Exposure to allergens induces the maturation of DCs with changes in morphology and presence of dendrites. Here, we demonstrate that the DCs in the lungs of ovalbumin (OVA)-sensitized and challenged mice are more mature owing to their pronounced dendrites than the DCs in the lungs and spleen of PBS-treated mice, which are immature and possess cytoplasmic veils. Intermediate to these two groups are the DCs in the Flt3 ligand-treated group that exhibit comparatively fewer dendrites and cytoplasmic veils and hence are classified as semimature. Presence of large numbers of well-developed mitochondria and rough endoplasmic reticulum in myeloid DCs from both lungs and spleen of OVA-sensitized and challenged mice indicate greater functional activity. Additionally, DCs from the OVA-sensitized and challenged mice also exhibit fat and glycogen stores, which are indicative of a mature population. In addition, treatment of the animals with Flt3 ligand attenuated airway hyperresponsiveness to methacholine in OVA-sensitized and challenged mice. These data suggest that morphological features could be indicative of the maturation and distinct functional state of DCs, and this could be associated with underlying mechanisms of Flt3 ligand-induced immunomodulation in allergic asthma.

Allergic airway inflammation.

Several genes, including ADAM33, DPP10, PHF11, GPRA, and TIM-1, have been implicated in the pathogenesis and susceptibility to atopy and asthma. Advances have been made in defining the mechanism for the control of allergic airway inflammation in response to inhaled antigens. There is growing evidence that associates asthma with a systemic propensity for allergic type 2 T-cell cytokines. Disordered coagulation and fibrinolysis could also exacerbate asthma symptoms. Major emphasis on immunotherapy for asthma during the past decade has been to direct the immune response to a type 1 response. Recent literature supports the pivotal role of plasmacytoid dendritic cells and allergen-specific T-regulatory cells in the development of tolerance to allergens. In this review article, we discuss the current information on the pathogenesis of allergic airway inflammation and potential allergen immunotherapies, which could be beneficial in the treatment of airway inflammation, allergy, and asthma.

Immunomodulation in asthma: a distant dream or a close reality?

The search for new treatments of asthma or any other disease for that matter is an infinite exercise. The scope for discovering new forms of treatment has increased now more than ever due to a better understanding of the molecular pathogenesis of the disease. Regulation of biomolecular or immunological events could occur at numerous points in the disease pathogenesis. This review describes the strategies to regulate the inappropriate immune responses that are elicited after exposure to an allergen. One such successful therapy is treatment with omalizumab, the anti-IgE antibody. Other therapies include cytokine antagonists, transcription factor antagonists, immunostimulatory DNA therapy, cytokine therapy and anti-T cell strategies. All these agents have been shown to be promising and could serve as an alternative approach to the treatment of asthma and maybe other allergic diseases.