Direct effects of interleukin-13 on signaling pathways for physiological responses in cultured human airway smooth muscle cells

Numerous studies have suggested an important role for the Th2 cytokines int erleukin (IL)-13 and IL-4 in the development of allergic asthma. We tested the hypothesis that IL-13 and IL-4 have direct effects on cultured airway s mooth muscle cells (HASM). Using RT-PCR, we showed that HASM cells express transcripts for IL-4 alpha, IL-13R alphaI, and IL-13R alpha II, but not for the common IL-2R gamma chain. We then analyzed the capacity of the two cyt okines to activate signaling pathways in HASM cells. Both IL-13 and IL-4 ca used STAT-6 phosphorylation, but the time course was different between the two cytokines, with peak effects occurring 15 min after addition of IL-4 an d 1 h after addition of IL-13. Effects on signaling were observed at cytoki ne concentrations as low as 0.3 ng/ml. IL-4 and IL-13 also caused phosphory lation of ERK MAP kinase. As suggested by the signaling studies, the biolog ical responses of the two cytokines were also different. We used magnetic t wisting cytometry to measure cell stiffness of HASM cells and tested the ca pacity of IL-4 and IL-13 to interfere with the reductions in cell stiffness induced by the beta -agonist isoproterenol (ISO). IL-13 (50 ng/ml for 24 h ), but not IL-4, significantly reduced beta -adrenergic responsiveness of H ASM cells, and the MEK inhibitor U0126 significantly reduced the effects of IL-13 on ISO-induced changes in cell stiffness. We propose that these dire ct effect of IL-13 on HASM cells may contribute at least in part to the air way narrowing observed in patients with asthma.