Loss of D1 and D2 dopamine receptors and muscarinic cholinergic receptors in rat brain following in vitro polytron homogenization.

The receptor specific binding of [3H]SCH23390 and [3H]spiperone to rat striatal membranes and [3H]QNB to rat cortical membranes was significantly reduced if the membrane suspensions were subjected to polytron homogenization. The degree of loss of the binding sites was a function of the polytron speed (setting) and the length of time of homogenization. Although the loss of binding sites could be reduced by maintaining a cold temperature of the tissue suspension during polytron homogenization, significant loss of binding sites could not be prevented. As many as 75% of the binding sites could be lost following polytron homogenization under the conditions employed in the present experiments. However, no significant change in the affinity of the remaining binding sites was observed. The loss of binding sites is not likely due to small tissue fragments passing through the filters. Care should be taken during tissue homogenization using a polytron or similar equipment to ensure that loss of receptor binding sites is minimized or remains constant between individual samples.

Acrolein-induced MUC5ac expression in rat airways.

Acrolein, a low-molecular-weight aldehyde found in photochemical smog and tobacco smoke, can induce mucus hypersecretion, inflammation, and airway hyperreactivity. To determine whether changes in steady-state mucin gene expression (MUC2 and MUC5ac) are associated with histological signs of mucus hypersecretion, rats were exposed to acrolein (3.0 parts/million, 6 h/day, 5 days/wk, 2 wk), and the trachea with the main stem bronchi was separated from the intrapulmonary airways (lung). The temporal expression of MUC2 and MUC5ac mRNA was determined by RT-PCR, and acidic mucin glycoproteins were detected by Alcian blue histochemical analysis. MUC5ac protein content in the airways was determined by immunohistochemical analysis. Tracheal MUC5ac mRNA increased within 2 days and was accompanied by an increase in MUC5ac immunostaining on the surface of the airways and in submucosal gland epithelium. By comparison, increases in lung MUC5ac mRNA and mucin glycoproteins were delayed and were elevated after exposures on days 5 and 9, respectively. Increased MUC5ac immunostaining was detected within the lumen and airway epithelium of the lung on day 12. In contrast, MUC2 mRNA levels were not significantly changed in the trachea or lung. These findings indicate that acrolein-induced mucus hypersecretion is due, in part, to increases in MUC5ac rather than to MUC2 gene expression. These findings suggest that aldehyde-induced increases in MUC5ac may play a role in chronic mucus hypersecretion, a pathognomonic feature of chronic obstructive pulmonary disease.

Regulation of human airway mucins by acrolein and inflammatory mediators.

Bronchitis, asthma, and cystic fibrosis, marked by inflammation and mucus hypersecretion, can be caused or exacerbated by airway pathogens or irritants including acrolein, an aldehyde present in tobacco smoke. To determine whether acrolein and inflammatory mediators alter mucin gene expression, steady-state mRNA levels of two airway mucins, MUC5AC and MUC5B, were measured (by RT-PCR) in human lung carcinoma cells (NCI-H292). MUC5AC mRNA levels increased after >/=0.01 nM acrolein, 10 microM prostaglandin E2 or 15-hydroxyeicosatetraenoic acid, 1.0 nM tumor necrosis factor-alpha (TNF-alpha), or 10 nM phorbol 12-myristate 13-acetate (a protein kinase C activator). In contrast, MUC5B mRNA levels, although easily detected, were unaffected by these agonists, suggesting that irritants and associated inflammatory mediators increase mucin biosynthesis by inducing MUC5AC message levels, whereas MUC5B is constitutively expressed. When transcription was inhibited, TNF-alpha exposure increased MUC5AC message half-life compared with control level, suggesting that transcript stabilization is a major mechanism controlling increased MUC5AC message levels. Together, these findings imply that irritants like acrolein can directly and indirectly (via inflammatory mediators) increase airway mucin transcripts in epithelial cells.

Monocyte inflammation augments acrolein-induced Muc5ac expression in mouse lung.

Acrolein, an unsaturated aldehyde found in smog and tobacco smoke, can induce airway hyperreactivity, inflammation, and mucus hypersecretion. To determine whether changes in steady-state mucin gene expression (Muc2 and Muc5ac) are associated with inflammatory cell accumulation and neutrophil elastase activity, FVB/N mice were exposed to acrolein (3.0 parts/million; 6 h/day, 5 days/wk for 3 wk). The levels of Muc2 and Muc5ac mRNA were determined by RT-PCR, and the presence of Muc5ac protein was detected by immunohistochemistry. Total and differential cell counts were determined from bronchoalveolar lavage (BAL) fluid, and neutrophil elastase activity was measured in the BAL fluid supernatant. Lung Muc5ac mRNA was increased on days 12 and 19, and Muc5ac protein was detected in mucous granules and on the surface of the epithelium on day 19. Lung Muc2 mRNA was not detected at measurable levels in either control or exposed mice. Acrolein exposure caused a significant and persistent increase in macrophages and a rapid but transient increase in neutrophils in BAL fluid. Recoverable neutrophil elastase activity was not significantly altered at any time after acrolein exposure. To further examine the role of macrophage accumulation in mucin gene expression, additional strains of mice (including a strain genetically deficient in macrophage metalloelastase) were exposed to acrolein for 3 wk, and Muc5ac mRNA levels and macrophage accumulation were measured. The magnitude of macrophage accumulation coincided with increased Muc5ac mRNA levels, indicating that excessive macrophage accumulation augments acrolein-induced Muc5ac synthesis and secretion after repeated exposure. These findings support a role for chronic monocytic inflammation in the pathogenesis of mucus hypersecretion observed in chronic bronchitis.

Ragweed-induced expression of GATA-3, IL-4, and IL-5 by eosinophils in the lungs of allergic C57BL/6J mice.

Allergen-induced recruitment of T lymphocytes and eosinophils to the airways is associated with increased expression of the transcription factor GATA-3. In this study, the relationship between airway inflammation and GATA-3 expression in the lungs was investigated using ragweed-sensitized C57BL/6J mice. Intratracheal ragweed challenge increased both the number of GATA-3-expressing cells in the perivascular and peribronchial regions and the amount of expression per cell. Interleukin (IL)-4 and IL-5 levels in bronchoalveolar lavage fluid were upregulated in parallel with GATA-3 expression. GATA-3 mRNA and protein colocalized to eosinophils. Eosinophils isolated from the lungs and stimulated with phorbol 12-myristate 13-acetate and/or A-23187 released IL-5. The release was inhibited by actinomycin D, which indicates that de novo synthesis of the cytokine was involved. Western blot analysis of proteins from isolated eosinophils demonstrated expression of the p50 subunit of nuclear factor-kappaB, a transcription factor that is implicated in control of GATA-3 expression. These data provide evidence that allergen challenge increases GATA-3 and proinflammatory cytokine expression by pulmonary eosinophils, which could provide positive feedback for the inflammatory response.

CD4(+) T cell-dependent airway mucus production occurs in response to IL-5 expression in lung.

The potential role of airway interleukin-5 (IL-5) expression in eliciting mucus production was demonstrated in a pulmonary IL-5 transgenic mouse model (NJ.1726) in which naive transgenic mice display comparable levels of airway mucus relative to allergen-sensitized and -challenged wild-type mice. The intrinsic mucus accumulation of NJ.1726 was abolished in compound transgenic-gene knockout mice deficient of either CD4(+) cells [NJ.1726/CD4(-/-)] or alphabeta T cell receptor-positive (TCR(+)) cells [NJ.1726/alphabeta TCR(-/-)]. In addition, mucus production in naive NJ.1726 was inhibited by >90% after administration of the soluble anti-IL-4 receptor alpha-subunit antagonist. The loss of mucus production in NJ.1726/CD4(-/-), NJ.1726/alphabeta TCR(-/-), and anti-IL-4 receptor alpha-subunit antagonist-treated mice occurred notwithstanding the significant pulmonary eosinophilia and expansion of airway B cells induced by ectopic IL-5 expression. Furthermore, the loss of mucus accumulation occurred in these mice despite elevated levels of airway and peripheral IL-5, indicating that IL-5 does not directly induce goblet cell metaplasia and mucus production. Thus pulmonary expression of IL-5 alone is capable of inducing CD4(+) T cell-dependent goblet cell metaplasia, apparently mediated by IL-4 receptor alpha-subunit-ligand interactions, and represents a previously unrecognized novel pathway for augmenting allergen-induced mucus production.

Blockade of CD49d inhibits allergic airway pathologies independent of effects on leukocyte recruitment.

Lymphocyte and/or eosinophil recruitment is dependent on the sequential interactions between adhesion molecules expressed on activated endothelial cells and both leukocyte subtypes. Endothelial P- and E-selectins mediate tethering and rolling of leukocytes through interactions with P-selectin glycoprotein ligand-1 (PSGL-1), and diapedesis subsequently occurs by engagement of endothelial vascular cell adhesion molecule-1 and CD49d (alpha(4)-integrins). The anti-inflammatory potential of interfering with these adhesive interactions was assessed with an ovalbumin challenge mouse model of asthma. Administration of a soluble form of PSGL-1 reduced eosinophils (80%) and lymphocytes (50%) in bronchoalveolar lavage fluid without affecting epithelial changes or airway hyperreactivity (AHR). In contrast, although administration of anti-CD49d monoclonal antibodies (PS/2) resulted in similar reductions in eosinophils (75%) and lymphocytes (50%), PS/2 reduced and abolished mucous cell metaplasia and AHR, respectively. Administration of both PSGL-1 and PS/2 had the additive effect of eliminating eosinophils from the airways (96% decrease), with few or no additional reductions (relative to PS/2 administration alone) in lymphocyte recruitment, mucous cell metaplasia, or AHR. These data show that eosinophils and lymphocytes differentially utilize adhesive interactions during recruitment and that the inhibition of AHR is independent of this recruitment.

Intrinsic AHR in IL-5 transgenic mice is dependent on CD4(+) cells and CD49d-mediated signaling.

Overexpression of interleukin (IL)-5 by the airway epithelium in mice using the rat CC10 promoter (NJ.1726 line) leads to several histopathologies characteristic of human asthma, including airway hyperreactivity (AHR). We investigated the contribution of B and T cells, as well as CD4 expression, to the development of AHR in IL-5 transgenic mice. NJ.1726 mice on a T cell or CD4 knockout background, but not on a B cell knockout background, lost intrinsic AHR. These effects occurred without decreases in IL-5 or eosinophils. We further investigated the contribution of alpha(4)-integrin signaling to the development of AHR in IL-5 transgenic mice through the administration of anti-CD49d (alpha(4)-integrin) antibody (PS/2). Administration of PS/2 resulted in immediate (16-h) inhibition of AHR. The inhibition of AHR was not associated with a decrease in airway eosinophils. These studies demonstrate that, despite the presence of increased levels of IL-5 and eosinophils in the lungs of NJ.1726 mice, CD4(+) cells and alpha(4)-integrin signaling are necessary for the intrinsic AHR that develops in IL-5 transgenic mice.

Ectopic expression of IL-5 identifies an additional CD4(+) T cell mechanism of airway eosinophil recruitment.

CD4(+) T cells have a critical role in the development of allergic pulmonary inflammation, including the recruitment of eosinophils to the airway lumen and interstitium. The expression of interleukin (IL)-5 by CD4(+) cells has, in particular, often been lionized as the central link between allergic inflammation and the concomitant expansion or recruitment of eosinophils. The mechanism(s) by which CD4(+) T cells mediates eosinophil recruitment was assessed with gene knockout mice deficient for T cells or T cell subtypes and a unique IL-5 transgenic mouse (line NJ.1726) that constitutively overexpresses this cytokine in the lung epithelium. Pulmonary IL-5 expression is significantly attenuated in T cell- and CD4(+) but not CD8(+) cell-deficient animals, suggesting an obvious explanation for the lack of eosinophils in the lungs of T cell-deficient and CD4(-/-) mice. However, although the constitutive expression of IL-5 in the lung epithelium of NJ.1726 mice elicited an eosinophilia in the airway lumen of both naive and ovalbumin-treated mice, in the absence of CD4(+) cells, allergen-mediated eosinophil recruitment to the bronchoalveolar lavage fluid was abolished. Moreover, intranasal instillation of the potent eosinophil-specific chemokine eotaxin-2 was incapable of eliciting eosinophil recruitment in naive and ovalbumin-treated NJ.1726 CD4(-/-) mice, suggesting that eosinophil trafficking during allergic inflammatory responses is a consequence of a CD4(+) cell-mediated event(s) in addition to IL-5 expression and the establishment of a pulmonary chemokine gradient.

Extensive eosinophil degranulation and peroxidase-mediated oxidation of airway proteins do not occur in a mouse ovalbumin-challenge model of pulmonary inflammation.

Paradigms of eosinophil effector function in the lungs of asthma patients invariably depend on activities mediated by cationic proteins released from secondary granules during a process collectively referred to as degranulation. In this study, we generated knockout mice deficient for eosinophil peroxidase (EPO) to assess the role(s) of this abundant secondary granule protein in an OVA-challenge model. The loss of EPO had no effect on the development of OVA-induced pathologies in the mouse. The absence of phenotypic consequences in these knockout animals extended beyond pulmonary histopathologies and airway changes, as EPO-deficient animals also displayed OVA-induced airway hyperresponsiveness after provocation with methacholine. In addition, EPO-mediated oxidative damage of proteins (e.g., bromination of tyrosine residues) recovered in bronchoalveolar lavage from OVA-treated wild-type mice was <10% of the levels observed in bronchoalveolar lavage recovered from asthma patients. These data demonstrate that EPO activities are inconsequential to the development of allergic pulmonary pathologies in the mouse and suggest that degranulation of eosinophils recruited to the lung in this model does not occur at levels comparable to those observed in humans with asthma.