Histologic stains have been used as the gold standard to visualize extracellular matrix (ECM) changes associated with airway remodeling in asthma, yet they provide no information on the biochemical and structural characteristics of the ECM, which are vital to understanding alterations in tissue function. In this work, we demonstrated the use of nonlinear optical microscopy (NLOM) and texture analysis algorithms to image fibrillar collagen (second harmonic generation) and elastin (two-photon excited autofluorescence), obtaining biochemical and structural information on the remodeled ECM environment in asthma.
We found that structural alterations are present in the airways of pediatric and adult lung donors, irrespective of fatal disease. In vitro studies demonstrated that asthmatic airway fibroblasts are deficient in their packaging of fibrillar collagen-I and that they express less decorin, important for collagen fibril packaging. Packaging of collagen fibrils was also found to be more disorganized in asthmatic airways compared with control subjects, using transmission electron microscopy. This study highlights the future potential clinical application of NLOM to assess airway remodeling in vivo.