Rationale The asthma susceptibility gene ADAM33/Adam33 is associated with bronchial hyperresponsiveness(BHR) in humans and mice. Soluble ADAM33 is increased in bronchoalveolar lavagefluid (BALF) of allergic asthma patients (Lee JY et al, AJRCCM 2006 Apr1; 173(7):729–35). Its levels correlate with declining FEV1%, suggesting a role in airway remodelling in asthma. Maternal allergy orexogenous IL-13 suppresses Adam33/ADAM33mRNA expression but enhances ADAM33 protein processing in human embryonic and juvenile mouse lungs (Haitchi HM et al, JACI. 2009 Sep; 124(3):590–7, 597). We hypothesise thatconditional expression of IL-13 in mouse lungs induces the enzymatically active, soluble form of ADAM33 in BALF, which is associated with BHR.
Methods IL-13 expression wasinduced using Doxycycline in CCSP-rtTA/Otet-Il-13 double-transgenic (dTg) mice. Methacholine challenge and lung function measurements were performed and lungswere harvested for mRNA extraction and immunohistochemistry (IHC). BALF was obtained forWestern-blotting for ADAM33 and testing of ADAM33 enzymatic activity using a fluorescenceresonance energy transfer (FRET) peptide assay.
Results There was asignificant increase in BHR to Methacholine in IL-13 expressing double transgenicmice. IHC showed an increase inbronchial smooth muscle in lungs of double transgenic mice. Similar to the RTqPCR findings in humanembryonic and juvenile mouse lungs, IL-13 suppressed Adam33 mRNA but no difference in a-smooth muscle actin (aSma) was evident. Immunoblotting for ADAMA33 in BALF demonstrateda 76kDa band, consistent with the ADAM33 ectodomain and processed forms at38/44kDa in dTg animals. ADAM33 enzymatic activity was also significantly increased.
Conclusion The data suggest thatallergic inflammation induced by IL-13 suppresses Adam33 mRNA expression but induces the release of soluble forms ofADAM33, yielding enzymatically active forms. The release of soluble forms may play a role in airway remodelling, potentiallyleading to BHR. We next propose to test the effect of specific ADAM33inhibitors on airway remodelling in this allergic mouse model to assess theirpotential as novel treatments for asthma.
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