John Kuchtey

Correlating Ca2+ Responses and Secretion in Individual RBL-2H3 Mucosal Mast Cells

The role of Ca2+ in stimulus-response coupling in nonexcitable cells is still not well understood. The Ca2+ responses of individual cells are extremely diverse, often displaying marked oscillations, and almost nothing is known about the specific features of these Ca2+signals that are important for the functional response of a cell. Using the RBL-2H3 mucosal mast cell as a model, we have studied the temporal relationship between changes in intracellular Ca2+ and serotonin secretion at the single-cell level using simultaneous indo-1 photometry and constant potential amperometry. Secretion in response to antigen never occurs until intracellular Ca2+ is elevated, nor is it seen during the first few oscillations in Ca2+. Exocytotic events tend to be clustered around the peaks of oscillations, but excellent secretion is also seen in cells with sustained elevations in Ca2+. Ca2+ release from stores in the absence of influx fails to elicit secretion. If refilling and continued release of Ca2+ from stores is prevented with thapsigargin, Ca2+ influx can still trigger secretion, suggesting that store-associated microdomains of Ca2+ are not required for exocytosis. Our findings demonstrate the importance of an amplitude-encoded Ca2+ signal and Ca2+influx for stimulus-secretion coupling in these nonexcitable cells.

Multiplex Cytokine Analysis Reveals Elevated Concentration of Interleukin-8 in Glaucomatous Aqueous Humor

PURPOSE To test the hypothesis that immune activation occurs in glaucoma by comparing concentrations of multiple cytokines in aqueous humor (AH) from patients with primary open angle glaucoma (POAG) and from cataract patients without glaucoma as controls. METHODS Cytokine concentrations in AH obtained during surgery were measured using microparticle-based immunoassays. Localized expression of IL-8 protein was investigated by immunohistochemistry of human eyes. RESULTS Eight cytokines (IL-1β, IL-2, IL-4, IL-5, IL-10, IL-12, IFN-γ, and TNF-α) were below the limits of detection, and two cytokines (IL-18 and IL-15) were detected at low levels or in only a few patients. Although IL-6 was detected in 26 of 30 control patients (median, 2.7 pg/mL) and in 23 of 29 POAG patients (median, 1.6 pg/mL), the difference was not statistically significant. IL-8 was detected in 28 of 30 control patients (median, 1.8 pg/mL) and in all 29 POAG patients (median, 4.9 pg/mL). The higher IL-8 concentration in the AH of POAG patients was statistically significant (P < 0.001). In pairs of eyes from patients with asymmetric glaucomatous optic nerve damage, IL-8 concentration was higher in the AH of the more severely affected eye (P < 0.05). Patients with severe visual field defects had higher IL-8 concentrations in the AH than did patients with mild visual field defects. IL-8 protein expression was found in human retina and optic nerve. CONCLUSIONS Concentration of the inflammatory cytokine IL-8 is significantly elevated in the AH of POAG patients, supporting the hypothesis that immune activation occurs in glaucoma.

Mapping of the Disease Locus and Identification of ADAMTS10 As a Candidate Gene in a Canine Model of Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is a leading cause of blindness worldwide, with elevated intraocular pressure as an important risk factor. Increased resistance to outflow of aqueous humor through the trabecular meshwork causes elevated intraocular pressure, but the specific mechanisms are unknown. In this study, we used genome-wide SNP arrays to map the disease gene in a colony of Beagle dogs with inherited POAG to within a single 4 Mb locus on canine chromosome 20. The Beagle POAG locus is syntenic to a previously mapped human quantitative trait locus for intraocular pressure on human chromosome 19. Sequence capture and next-generation sequencing of the entire canine POAG locus revealed a total of 2,692 SNPs segregating with disease. Of the disease-segregating SNPs, 54 were within exons, 8 of which result in amino acid substitutions. The strongest candidate variant causes a glycine to arginine substitution in a highly conserved region of the metalloproteinase ADAMTS10. Western blotting revealed ADAMTS10 protein is preferentially expressed in the trabecular meshwork, supporting an effect of the variant specific to aqueous humor outflow. The Gly661Arg variant in ADAMTS10 found in the POAG Beagles suggests that altered processing of extracellular matrix and/or defects in microfibril structure or function may be involved in raising intraocular pressure, offering specific biochemical targets for future research and treatment strategies.

Enhancement of Dendritic Cell Antigen Cross-Presentation by CpG DNA Involves Type I IFN and Stabilization of Class I MHC mRNA

Dendritic cells (DCs) internalize exogenous Ags and process them for cross-presentation by class I MHC (MHC-I) to CD8+ T cells. This processing can occur by transporter for Ag presentation (TAP)-dependent or TAP-independent mechanisms. We observed that CpG DNA enhanced cross-presentation of Ags by Flt-3L-cultured bone marrow-derived murine DCs by a type I IFN (IFN-αβ)-dependent mechanism. Myeloid DCs provided cross-presentation function in this system. Both TAP1 knockout and wild-type DCs showed enhanced cross-presentation when treated with CpG DNA at 26°C, demonstrating that TAP is not essential to this regulatory mechanism, although TAP is an important determinant of MHC-I expression. Enhancement of cross-processing by CpG DNA did not involve increased Ag uptake or proteolysis but did correlate with IFN-αβ-dependent increases in expression of MHC-I mRNA and protein. Increased MHC-I mRNA levels resulted in part from stabilization of MHC-I mRNA, a novel posttranscriptional mechanism for regulation of MHC-I expression. Thus, a major mechanism by which CpG oligodeoxynucleotide increase cross presentation by DCs appears to be an IFN-αβ-mediated increase in MHC-I synthesis.

CpG‐B ODNs potently induce low levels of IFN‐αβ and induce IFN‐αβ‐dependent MHC‐I cross‐presentation in DCs as effectively as CpG‐A and CpG‐C ODNs

Deoxycytidyl‐deoxyguanosine [(CpG)3] oligodeoxynucleotides (ODNs) signal through TLR9 to induce type‐I IFN (IFN‐αβ) and IFN‐αβ‐dependent MHC‐I cross‐presentation of exogenous antigens by dendritic cells (DCs). A puzzle was presented by our observation that three ODN classes, CpG‐A, CpG‐B, and CpG‐C, had similar efficacy for induction of IFN‐αβ‐dependent MHC‐I antigen cross‐presentation by myeloid DCs despite greatly differing for induction of IFN‐αβ (CpG‐A>CpG‐C>>CpG‐B). All ODN classes similarly enhanced plasmacytoid DC (pDC) presentation of exogenous MHC‐I‐restricted peptide, although pDCs did not cross‐process protein antigen. MHC‐I and the transporter for antigen presentation were induced by all ODN classes or IFN‐α. CpG‐B ODNs were slightly more potent than CpG‐A or CpG‐C ODNs for induction of low levels of IFN‐αβ but less efficacious at high concentrations than CpG‐A or CpG‐C ODNs. Low levels of IFN‐αβ induced by CpG‐B ODNs sufficed for full induction of MHC‐I cross‐presentation. Thus, CpG‐B ODNs are slightly more potent but less efficacious than CpG‐A and CpG‐C ODNs for induction of IFN‐αβ. High sensitivity to IFN‐αβ allows CpG‐B ODNs to be equally efficacious for induction of MHC‐I cross‐presentation. CpG‐B ODNs may be effective for inducing therapeutic responses that require low levels of IFN‐αβ and may avoid unnecessarily high induction of IFN‐αβ.

Angiopoietin-like 7 secretion is induced by glaucoma stimuli and its concentration is elevated in glaucomatous aqueous humor.

PURPOSE To investigate the possibility that Angiopoietin-like 7 (ANGPTL7) protein is involved in the pathogenesis of glaucoma. METHODS Primary human trabecular meshwork (TM) cells and corneoscleral explants were stimulated with either dexamethasone (DEX) or transforming growth factor beta (TGFbeta), and ANGPTL7 protein secreted into culture medium was determined by Western blot analysis. The effect of stable overexpression of ANGPTL7 in transfected immortalized TM cell lines on collagen expression was investigated by immunocytochemistry. Localization of ANGPTL7 protein in human eyes was determined by immunohistochemistry. The concentration of ANGPTL7 protein in aqueous humor (AH) from patients with glaucoma and control patients was compared by Western blot analysis. The beagle model of primary open-angle glaucoma (POAG) was used to correlate ANGPTL7 protein levels in canine AH with disease progression. RESULTS TGFbeta and DEX stimulated secretion of ANGPTL7 protein by TM cells and corneoscleral explants. Overexpression of ANGPTL7 by immortalized TM cell lines increased expression of type I collagen. Expression of ANGPTL7 protein was located in the corneal stroma, near the limbus, and throughout the sclera, with lower expression in the TM. In the lamina cribrosa, ANGPTL7 expression was associated with the cribriform plates. The concentration of ANGPTL7 protein was elevated in AH from patients with glaucoma and increased as disease progressed in POAG beagle dogs. CONCLUSIONS Induction of ANGPTL7 secretion by glaucoma stimuli and increased concentration of ANGPTL7 in glaucomatous AH suggest that ANGPTL7 is overexpressed in glaucoma. Since overexpression of ANGPTL7 increases collagen expression, a potential disease mechanism, ANGPTL7 could have a pathogenic role in glaucoma, and may serve as a potential therapeutic target.

The Microfibril Hypothesis of Glaucoma: Implications for Treatment of Elevated Intraocular Pressure

Microfibrils are macromolecular aggregates located in the extracellular matrix of both elastic and nonelastic tissues that have essential functions in formation of elastic fibers and control of signaling through the transforming growth factor beta (TGFβ) family of cytokines. Elevation of systemic TGFβ and chronic activation of TGFβ signal transduction are associated with diseases caused by mutations in microfibril-associated genes, including FBN1. A role for microfibrils in glaucoma is suggested by identification of risk alleles in LOXL1 for exfoliation glaucoma and mutations in LTBP2 for primary congenital glaucoma, both of which are microfibril-associated genes. Recent identification of a mutation in another microfibril-associated gene, ADAMTS10, in a dog model of primary open-angle glaucoma led us to form the microfibril hypothesis of glaucoma, which in general states that defective microfibrils may be an underlying cause of glaucoma. Microfibril defects could contribute to glaucoma through alterations in biomechanical properties of tissue and/or through effects on signaling through TGFβ, which is well established to be elevated in the aqueous humor of glaucoma patients. Recent work has shown that diseases caused by microfibril defects are associated with increased concentrations of TGFβ protein and chronic activation of TGFβ-mediated signal transduction. In analogy with other microfibril-related diseases, defective microfibrils could provide a mechanism for the elevation of TGFβ2 in glaucomatous aqueous humor. If glaucoma shares mechanisms with other diseases caused by defective microfibrils, such as Marfan syndrome, therapeutic interventions to inhibit chronic activation of TGFβ signaling used in those diseases may be applied to glaucoma.

Interferon‐αβ mediates partial control of early pulmonary Mycobacterium bovis bacillus Calmette–Guérin infection

The role of type I interferon (IFN‐αβ) in modulating innate or adaptive immune responses against mycobacterial infection in the lung is unclear. In this study we investigated the susceptibility of IFN‐αβ‐receptor‐deficient (IFN‐αβR–/–) mice to pulmonary infection with aerosolized Mycobacterium bovis bacillus Calmette–Guérin (BCG). During early infection (2–3 weeks), enhanced growth of BCG was measured in the lungs of IFN‐αβR–/– mice compared to wild‐type mice. However, during late infection the burden of BCG was similar in the lungs of IFN‐αβR–/– and wild‐type mice. Although control of BCG growth was delayed, recruitment and activation of T and natural killer cells, production of IFN‐γ, and cytokine expression were all similar in wild‐type and IFN‐αβR–/– mice. However, decreased expression of nitric oxide in bronchoalveolar lavage fluids from IFN‐αβR–/– mice correlated with enhanced growth of BCG. Bone marrow‐derived macrophages from IFN‐αβR–/– mice also produced less nitric oxide following infection with BCG in vitro. These findings suggest that IFN‐αβ contributes to innate immunity to pulmonary mycobacterial infection by augmenting production of nitric oxide.

CpG DNA Induces a Class II Transactivator-Independent Increase in Class II MHC by Stabilizing Class II MHC mRNA in B Lymphocytes

Microbial products, such as CpG DNA and LPS, enhance class II MHC (MHC-II) expression and Ag presentation by dendritic cells, but this effect does not occur with macrophages and is largely unexplored in B cells. Although MHC-II expression is influenced by transcriptional regulation, which is governed by class II transactivator (CIITA) in all cells, microbial products enhance MHC-II expression by dendritic cells in part by increasing MHC-II protein stability. In this study, we show that the CpG-induced increase in MHC-II expression by B lymphocytes is not due to protein stabilization or changes in CIITA expression or activity, but instead is due to increased stability of MHC-II mRNA. This CIITA-independent mechanism adds a new layer of complexity to regulation of MHC-II and may increase T cell help for B cell Ab responses to microbial or vaccine Ags.

CpG-B Oligodeoxynucleotides Inhibit TLR-Dependent and -Independent Induction of Type I IFN in Dendritic Cells

CpG oligodeoxynucleotides (ODNs) signal through TLR9 to induce type I IFN (IFN-αβ) in dendritic cells (DCs). CpG-A ODNs are more efficacious than CpG-B ODNs for induction of IFN-αβ. Because IFN-αβ may contribute to autoimmunity, it is important to identify mechanisms to inhibit induction of IFN-αβ. In our studies, CpG-B ODN inhibited induction of IFN-αβ by CpG-A ODN, whereas induction of TNF-α and IL-12p40 by CpG-A ODN was not affected. CpG-B inhibition of IFN-αβ was observed in FLT3 ligand-induced murine DCs, purified murine myeloid DCs, plasmacytoid DCs, and human PBMCs. CpG-B ODN inhibited induction of IFN-αβ by agonists of multiple receptors, including MyD88-dependent TLRs (CpG-A ODN signaling via TLR9, or R837 or Sendai virus signaling via TLR7) and MyD88-independent receptors (polyinosinic:polycytidylic acid signaling via TLR3 or ds break-DNA signaling via a cytosolic pathway). CpG-B ODN did not inhibit the IFN-αβ positive feedback loop second-wave IFN-αβ, because IFN-αβ–induced expression of IFN-αβ was unaffected, and CpG-B inhibition of IFN-αβ was manifested in IFN-αβR−/− DCs, which lack the positive feedback mechanism. Rather, CpG-B ODN inhibited early TLR-induced first wave IFN-α4 and IFN-β. Chromatin immunoprecipitation revealed that association of IFN regulatory factor 1 with the IFN-α4 and IFN-β promoters was induced by CpG-A ODN but not CpG-B ODN. Moreover, CpG-A–induced association of IFN regulatory factor 1 with these promoters was inhibited by CpG-B ODN. Our studies demonstrate a novel mechanism of transcriptional regulation of first-wave IFN-αβ that selectively inhibits induction of IFN-αβ downstream of multiple receptors and may provide targets for future therapeutic inhibition of IFN-αβ expression in vivo.