Airway hyperresponsiveness to bronchoconstrictor agonists and hyporesponsiveness to bronchodilator beta-agonists are characteristic features of human asthma. Current evidence favors a causal link between the airway inflammation and altered airway responsiveness of asthma. Cytokines released in the asthmatic airway may provide this link. These cytokines not only have the capacity to modulate the complement and level of activation of immune/inflammatory cells in the airways, but also appear to alter airway responses to agonists. For example, each of the """"""""pro- asthmatic"""""""" cytokines IL-1beta, TNFalpha, IL-2, IL-4, and IL-5, proposed for study, is present in increased quantities in the asthmatic airway and has been shown to result in airway hyperresponsivemness in animals in vivo. It is our hypothesis that these cytokines have direct effects on airway smooth muscle responses resulting in decreased responses to dilator stimuli and increased responses to contractile stimuli. We propose to examine this hypothesis and to determine the mechanism of action of these cytokines using human airway smooth muscle (HASM) cells in culture. A novel technique, magnetic twisting cytometry, that provides a mechanical index of smooth muscle response, cytoskeletal stiffness, will be combined with measurements of Ca++ or cAMP, providing a system that allows for determination of the site in the pathway leading from receptor activation to smooth muscle contraction/relaxation that may be altered by cytokines. A culture system also allows for generation of sufficient quantities of functional cells with which to perform biochemical or molecular biological analyses in order to further examine the mechanism of action of cytokines.
Four specific aims will be pursued; 1) Measure the dose and time related effects of """"""""pro-asthmatic"""""""" cytokines on HASM cell stiffness and cAMP formation in response to isoproterenol and prostaglandin E2 (PGE2); 2) Test the hypothesis that cytokines decrease beta-adrenergic responses by increasing prostaglandin G/H synthase (PGHS) expression leading to increased PGE2 formation, EP3 prostanoid receptor activation of G1 and inhibition of adenylyl cyclase by measuring PGHS-2 and Gia expression, and by use of PGHS-2 and Gi inhibitors, and EP3 receptor agonists; 3) Measure the dose and time related effects of """"""""pro-asthmatic"""""""" cytokines on changes in HASM cell stiffness and intracellular calcium induced by agonists believed to be of importance in the asthmatic lesion, namely histamine, acetylcholine, and substance P, and 4) Test the hypothesis that cytokines increase HASM cell stiffness responses to contractile agonists by increasing the activation of phospholipase C (PLC), by measuring IP3 formation by contractile agonists and PLC activity. Demonstration of the role and mechanism of action of cytokines in leading to beta-adrenergic receptor dysfunction may provide new avenues for improvements in the safe and efficacious use of these agents. Demonstration of the role and mechanism of action of cytokines in augmenting airway smooth muscle responses to contractile agonist may allow us to develop new models of intervention to prevent the induciton of airway hyperresponsiveness, and thereby limit the capacity of the airways to narrow during an asthmatic episode.
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