Serum integrin accumulation during asthma exacerbation: The role of matrix metalloproteinases

The inflammation caused by asthma exacerbation can lead to permanent changes in the airways and loss of lung function. Integrins are membrane receptors that interact with components of the extracellular matrix and cell adhesion molecules. It is known that these receptors can be found in soluble form in some conditions such as asthma, but it is unknown if exacerbation during asthma leads to soluble integrins. Our results indicated that asthma patients showed higher levels of soluble α1, α2, and β2 integrin subunits in their serum compared to controls, as confirmed by both ELISA and western blot. During asthma exacerbation, the levels of α2 and β2 integrin subunits increased even more compared to non-exacerbation and controls, while the α1 integrin subunit decreased. Western blot analysis identified two β2 integrin subunits, one at 75 kDa and another at 120 kDa; the 120 kDa subunit increased during asthma exacerbation. The activity of matrix metalloproteinase 9 (MMP9) increased during exacerbation, while MMP2 remained unchanged. Lower forced expiratory volume in 1 second (FEV1) values were associated with higher expression levels of α2, β1, and β2 integrin subunits. Active and latent MMP9 were correlated with the levels of the β2 integrin subunit, which means that at low levels of active and latent MMP9, there are lower levels of β2 integrin subunit. In conclusion, asthma exacerbation leads to the presence of soluble integrins, particularly the β2 subunit, most likely due to MMP9-induced proteolytic cleavage.