Biomedical subjects

Jared M Brown

Publications and source records attributed to Jared M Brown.

6 recordsLinked to original sources

PubMed2006

5-hydroxytryptamine induces mast cell adhesion and migration.

The neurotransmitter serotonin (5-hydroxytryptamine (5-HT)) is implicated in enhancing inflammatory reactions of skin, lung, and gastrointestinal tract. To determine whether 5-HT acts, in part, through mast cells (MC), we first established that mouse bone marrow-derived MC (mBMMC) and human CD34(+)-derived MC (huMC) expressed mRNA for multiple 5-HT receptors. We next determined the effect of 5-HT on mouse and human MC degranulation, adhesion, and chemotaxis. We found no evidence that 5-HT degranulates MC or modulates IgE-dependent activation. 5-HT did induce mBMMC and huMC adherence to fibronectin; and immature and mature mBMMC and huMC migration. Chemotaxis was accompanied by actin polymerization. Using receptor antagonists and pertussis toxin, we identified 5-HT(1A) as the principal receptor mediating the effects of 5-HT on MC. mBMMC from the 5-HT(1A) receptor knockout mouse (5-HT(1A)R(-/-)) did not respond to 5-HT. 5-HT did induce accumulation of MC in the dermis of 5-HT(1A)R(+/+) mice, but not in 5-HT(1A)R(-/-) mice. These studies are the first to demonstrate an effect of 5-HT on MC. Furthermore, both mouse and human MC respond to 5-HT through the 5-HT(1A) receptor. Our data are consistent with the conclusion that 5-HT promotes inflammation by increasing MC at the site of tissue injury.

Actins↗

PubMed2006

Silica-directed mast cell activation is enhanced by scavenger receptors.

Inhalation of crystalline silica results in pulmonary fibrosis and silicosis. It has been suggested that mast cells play a role in these conditions. How mast cells would influence pathology is unknown. We thus explored mast cell interactions with silica in vitro and in B6.Cg-kit(W-sh) mast cell-deficient mice. B6.Cg-kit(W-sh) mice did not develop inflammation or significant collagen deposition after instillation of silica, while C57Bl/6 wild-type mice did have these findings. Given this supporting evidence of a role for mast cells in the development of silicosis, we examined the ability of silica to activate mouse bone marrow-derived mast cells (BMMC), including degranulation (beta-hexosaminidase release); production of reactive oxygen species (ROS) and inflammatory mediators; and the effects of silica on Fc epsilon RI-dependent activation. Silica did not induce mast cell degranulation. However, TNF-alpha, IL-13, monocyte chemotactic protein-1, protease activity, and production of ROS were dose-dependently increased after silica exposure, and production was enhanced after Fc epsilon RI stimulation. This mast cell activation was inhibited by anti-inflammatory compounds. As silica mediates some effects in macrophages through scavenger receptors (SRs), we first determined that mast cells express scavenger receptors; then explored the involvement of SR-A and macrophage receptor with colleagenous structure (MARCO). Silica-induced ROS formation, apoptosis, and TNF-alpha production were reduced in BMMC obtained from SR-A, MARCO, and SR-A/MARCO knockout mice. These findings demonstrate that silica directs mast cell production of inflammatory mediators, in part through SRs, providing insight into critical events in the pathogenesis and potential therapeutic targets in silicosis.

Animals↗

PubMed2005

Effects of rottlerin on silica-exacerbated systemic autoimmune disease in New Zealand mixed mice.

Environmental crystalline silica exposure has been associated with formation of autoantibodies and development of systemic autoimmune disease, but the mechanisms leading to these events are unknown. Silica exposure in autoimmune-prone New Zealand mixed (NZM) mice results in a significant exacerbation of systemic autoimmunity as measured by increases in autoantibodies and glomerulonephritis. Previous studies have suggested that silica-induced apoptosis of alveolar macrophages (AM) contributes to the generation of the autoantibodies and disease. Rottlerin has been reported to inhibit apoptosis in many cell types, possibly through direct or indirect effects on PKCdelta. In this study, rottlerin reduced silica-induced apoptosis in bone marrow-derived macrophages as measured by DNA fragmentation. In NZM mice, RNA and protein levels of PKCdelta were significantly elevated in AM 14 wk after silica exposure. Therefore, rottlerin was used to reduce apoptosis of AM and evaluate the progress of silica-exacerbated systemic autoimmune disease. Fourteen weeks after silica exposure, NZM mice had increased levels of anti-histone autoantibodies, high proteinuria, and glomerulonephritis. However, silica-instilled mice that also received weekly instillations of rottlerin had significantly lower levels of proteinuria, anti-histone autoantibodies, complement C3, and IgG deposition within the kidney. Weekly instillations of rottlerin in silica-instilled NZM mice also inhibited the upregulation of PKCdelta in AM. Together, these data demonstrate that in vivo treatment with rottlerin significantly decreased the exacerbation of autoimmunity by silica exposure.

Acetophenones↗

PubMed2004

Silica-exposed mice generate autoantibodies to apoptotic cells.

Silica exposure has been associated with development of autoantibodies and systemic autoimmune disease, but mechanisms leading to these events are unknown. This study tested the hypothesis that autoantibodies associated with silica exposure may recognize epitopes on apoptotic macrophages. Serum was obtained from New Zealand mixed (NZM) mice, in which instillation of silica significantly increased production of autoantibodies. Sera were selected that were shown, by indirect immunofluorescence (IIF), to be positive or negative for antinuclear antibodies (ANA) following silica or saline exposure, respectively. Apoptosis was induced in MH-S murine macrophages using silica or cycloheximide. The ability of the autoantibodies to preferentially recognize apoptotic cells was tested using IIF and ELISA. Apoptotic cells, but not live cells, were shown to stain with serum from ANA-positive mice, but not from ANA-negative serum. In addition, binding of antibodies from ANA-positive mice was shown to be significantly greater on cellular lysates from apoptotic cells, but not necrotic or live cell lysates using an ELISA based assay. Finally, inhibition of apoptosis with a broad spectrum caspase inhibitor, Boc-D-FMK, blocked the increased binding by the autoantibodies. These results suggest that autoantibodies from mice with silica-exacerbated autoimmune responses recognize specific epitopes on apoptotic macrophages. It is therefore possible that silica-induced apoptosis may exacerbate autoimmune responses by exposing antigenic epitopes to the immune system.

Administration, Intranasal↗

PubMed2004

CR1/CR2 deficiency alters IgG3 autoantibody production and IgA glomerular deposition in the MRL/lpr model of SLE.

CR1 and CR2 expression is decreased by approximately 50% on B cells of patients with systemic lupus erythematosus (SLE). Expression is also decreased in the MRL/lpr murine model of SLE prior to the development of clinical disease, suggesting that this alteration may play a role in pathogenesis. To determine whether the decrease in receptor levels affects the development of SLE, we analyzed MRL/lpr mice in which CR1/CR2 expression was altered by gene targeting. Mice from each cohort (Cr2+/+, Cr2+/-, and Cr2-/-) were analyzed biweekly for the development of proteinuria and autoantibodies. Kidneys were examined at 12 and 16 weeks for evidence of immune complex deposition and renal disease. Deficiency of CR1/CR2 did not affect survival or development of renal disease as measured by proteinuria. Mice deficient in CR1/CR2 had significantly lower levels of IgG3 rheumatoid factor (RF) and total serum IgG3, suggesting a specific defect in production of IgG3 in response to endogenous autoantigens. Since IgG3 RF has been associated with the development of vasculitis in this model, we examined the mice for alterations in development of this clinical manifestation. Although there was no difference in the development of ear necrosis among the three groups, renal arteritis was not identified in any of the Cr2+/- mice, whereas it was present in 20% of the Cr2+/- and 40% of the Cr2+/+ mice. Finally, significantly higher levels of IgA were seen in the glomeruli of Cr2+/- mice compared to Cr2+/- or Cr2+/+ mice, suggesting that CR1/CR2 are involved in either the regulation of IgA production or the clearance of IgA immune complexes. Together these data support the concept that alterations in CR1/CR2 expression or function affect the regulation of autoantibody production and/or clearance and may have clinical consequences.

Animals↗

PubMed2004

Immunoglobulin and lymphocyte responses following silica exposure in New Zealand mixed mice.

Epidemiological studies have shown strong associations between silica exposure and several autoimmune diseases, including scleroderma and systemic lupus erythematosus. We previously reported that the New Zealand mixed (NZM) mouse develops silicosis and exacerbated autoimmunity following crystalline silica exposure, including increased levels of autoantibodies, proteinuria, circulating immune complexes, pulmonary fibrosis, and glomerulonephritis. In this study, the NZM mouse was used to examine changes in immune activation following silica exposure by measuring levels of immunoglobulin, cytokines and lymphocyte populations. Levels of immunoglobulin (Ig) G1 were significantly decreased from 1124 +/- 244 microg/ml in saline exposed mice to 614 +/- 204 microg/ml in silica-exposed mice, suggesting a decrease in the Th2 response. The levels of tumor necrosis factor (TNF)-alpha were significantly increased (1.5-fold) in the bronchoalveolar lavage fluid of the silica-exposed mice as compared to the saline-exposed mice. The number of B1a B cells were significantly increased sixfold within the superficial cervical lymph nodes of silica-exposed mice as compared with saline-exposed mice. Following silica exposure, CD4+ T cells significantly increased threefold within the superficial cervical lymph nodes. During this increase in the number of CD4+ T cells, the number of CD4+CD25+ regulatory T cells was not significantly changed, altering the ratio of regulatory T cells to T helper cells from 1:5 to 1:8 following silica exposure. Therefore, the silica-induced alterations in immunoglobulin levels, increased TNF-alpha, increased B1a B cells and CD4+ T cells, with decreased regulatory T cells, may provide an environment that allows for increased autoreactivity. These studies begin to provide possible mechanisms for environmentally induced autoimmune diseases that have been reported in many epidemiological studies.

Animals↗