EFFECT OF IL-1-BETA ON RESPONSES OF CULTURED HUMAN AIRWAY SMOOTH-MUSCLE CELLS TO BRONCHODILATOR AGONISTS

Decreased beta-adreneric responsiveness is a characteristic feature of asthma. In order to determine whether cytokines released in the asthm atic airway contribute to this phenomenon, we measured changes in stif fness of cultured human airway smooth muscle (HASM) cells induced by i soproterenol (ISO) in control HASM cells and HASM cells pretreated wit h IL-1 beta (20 ng/ml for approximately 42 h). Stiffness was measured by magnetic twisting cytometry. HASM cells were obtained from normal t racheal tissue obtained at lung transplant, and studied in passages 4- 7. In control cells, ISO caused a dose-related decrease in cell stiffn ess. IL-1 beta had no effect on baseline cell stiffness. However, IL-1 beta caused a rightward shift in the concentration-response curve to ISO and decreased the maximal effectiveness of this agonist. Decreased responses to ISO were also obtained with 2 ng/ml IL-1 beta, or when c ells were pretreated with IL-1 beta (20 ng/ml, for 22 h. This effect o f IL-1 beta was not altered by pretreatment of the cells with pertussi s toxin (100 ng/ml throughout the IL-1 beta exposure period). IL-1 bet a also significantly attenuated the ability of prostaglandin E-2 (PGE( 2)) to decrease cell stiffness. In contrast, IL-1 beta had no affect o n cell stiffness responses to dibutryl cAMP, a cell permeant analog of cAMP suggesting that the cytokine does not influence either the abili ty of cAMP to activate kinases, or the targets of these kinases which ultimately mediate cell relaxation., IL-1 beta (20 ng/ml for 40 h) cau sed a small (30%) but significant (P < 0.02) increase in basal cAMP, b ut also resulted in a 2-3-fold decrease in the changes in cAMP formati on induced by either ISO or PGE(2). In contrast, IL-1 beta had no effe ct on cAMP formation in response to forskolin. suggesting that IL-1 be ta does not mediate its effects via changes in the expression or activ ity of adenylyl cyclase. pretreatment with IL-1 beta had no significan t effect on beta(2) adrenoceptor number assessed by [I-125]-CYP bindin g in these cells, nor was there any significant effect of IL-1 beta on G(s alpha) expression assessed by Western blot. In summary, our resul ts indicate that IL-1 beta causes a concentration- and time-dependent decrease in responses of HASM cells to ISO and are consistent with the hypothesis that the effects of IL-1 beta are mediated by uncoupling o f beta-receptors from G(s)-induced activation of adenylyl cyclase.