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TRANSLATIONAL PHYSIOLOGY

TGF- potentiates airway smooth muscle responsiveness to bradykinin

¹Pulmonary, Allergy, and Critical Care Division, Department of Medicine, University of Pennsylvania School of Medicine; ²The Wistar Institute, Philadelphia, Pennsylvania; and ³Ludwig Institute for Cancer Research, New York, New York

Submitted 18 January 2005 ; accepted in final form 18 May 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 TGF- can modulate bradykinin-associated bronchial hyperresponsiveness. To test whether TGF- directly modulates airway smooth muscle (ASM) responsiveness to bradykinin, isolated murine tracheal rings were used to assess whether TGF- alters 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 TGF- on bradykinin-evoked calcium signals since calcium is a key molecule regulating ASM excitation-contraction 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 TGF- treatment 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 TGF- may 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.

airway hyperresponsiveness; airway remodeling; intracellular calcium; isometric force generation; transforming growth factor-

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