TGF- potentiates airway smooth muscle responsiveness to bradykinin

Kim, Jenny H., Deepika Jain, Omar Tliba, Bei Yang, William F. Jester, Jr., Reynold A. Panettieri, Jr., Yassine Amrani, and Ellen Puré. TGFpotentiates airway smooth muscle responsiveness to bradykinin. Am J Physiol Lung Cell Mol Physiol 289: L511–L520, 2005. First published May 27, 2005; doi:10.1152/ajplung.00027.2005.—The molecular mechanisms by which bradykinin induces excessive airway obstruction in asthmatics remain unknown. Transforming growth factor (TGF)has been involved in regulating airway inflammation and remodeling in asthma, although it is unknown whether TGFcan modulate bradykinin-associated bronchial hyperresponsiveness. To test whether TGFdirectly modulates airway smooth muscle (ASM) responsiveness to bradykinin, isolated murine tracheal rings were used to assess whether TGFalters ASM contractile responsiveness to bradykinin. Interestingly, we found TGF-treated murine rings (12.5 ng/ml, 18 h) exhibited increased expression of bradykinin 2 (B2) receptors and became hyperreactive to bradykinin, as shown by increases in maximal contractile responses and receptor distribution. We investigated the effect of TGFon bradykinin-evoked calcium signals since calcium is a key molecule regulating ASM excitationcontraction coupling. We reported that TGF, in a dose(0.5–10 ng/ml) and time(2–24 h) dependent manner, increased mRNA and protein expression of the B2 receptor in cultured human ASM cells. Maximal B2 receptor protein expression that colocalized with CD44, a marker of membrane cell surface, occurred after 18 h of TGFtreatment and was further confirmed using fluorescence microscopy. TGF(2.5 ng/ml, 18 h) also increased bradykinin-induced intracellular calcium mobilization in fura-2-loaded ASM cells. TGF-mediated enhancement of calcium mobilization was not attenuated with indomethacin, a cyclooxygenase inhibitor. These data demonstrate for the first time that TGFmay play a role in mediating airway hyperresponsiveness to bradykinin seen in asthmatics by enhancing ASM contractile responsiveness to bradykinin, possibly as a result of increased B2 receptor expression and signaling.