SIGNAL TRANSDUCTION IN SENSITIZED AIRWAY SMOOTH MUSCLE

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DESCRIPTION: This investigation proposes to examine the exaggerated airway narrowing response and impaired beta-adrenoceptor inhibitory response in a model of human asthma. Given the role of the key intracellular second messenger, IP3 in regulating airway smooth muscle (ASM) contractility, as well as the role of certain pro-inflammatory cytokines in mediating the atopic/asthmatic state, two interrelated hypotheses are raised: 1. Changes in constrictor agonists and beta-adrenoceptor mediated responsiveness in atopic/asthmatic ASM are attributed to altered receptor coupled accumulation and/or action of IP3; and 2. The induction of these changes in transmembrane signaling regulation ASM responsiveness is related to Fc receptor-coupled autocrine release and action of specific cytokines in ASM. In addressing these hypotheses, mechanism regulating contractility, receptor and G protein expression, second messenger activation, and cytokine expression and action will be examined in isolated rabbit and human ASM tissue and cultured ASM cells passively sensitized with human atopic/asthmatic serum. To investigate mechanisms underlying altered ASM contractility in the sensitized state, the investigators will examine changes in 1) agonist/receptor-coupled accumulation of IP3; 2) expression and modulatory action of specific G proteins; and 3) the metabolism and binding of IP3 to its Ca2+ mobilizing intracellular receptor. To investigate mechanisms underlying attenuated beta-adrenoceptor-coupled relaxation in sensitized ASM, the investigators propose to examine changes in 1) specific G protein expression and regulation of beta-adrenergic receptor biding and transduction; and 2) beta-adrenoceptor/G protein-coupled modulation of constrictor agonist-induced accumulation on IP3, its metabolism, and its receptor binding. Finally, to address the autorcrine role of cytokines in inducing altered ASM responsiveness in the atopic/asthmatic sensitized state, the investigators will examine whether 1) atopic sensitization of ASM induces the autocrine expression and action of specific cytokines; 2) the latter is attributed to activation of endogenously upregulated Fc receptors on ASM cells; and 3) cytokine-induced changes in ASM responsiveness reflect alterations in the contributions of the separate mechanisms delineated above under objectives cited above. Collectively, these studies should yield important new insights into the potential autocrine role of ASM in the mechanistic interplay between Fc receptor activation, cytokine activation, and altered transmembrane signaling contributing to altered ASM responsiveness in the atopic/asthmatic sensitized state.