Defective Fibrillar Collagen Organization by Fibroblasts Contributes to Airway Remodeling in Asthma

RATIONALE: Histological 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. OBJECTIVE: Demonstrate the use of non-linear optical microscopy (NLOM) and texture analysis algorithms to image fibrillar collagen (Second harmonic generation) and elastin (Two-photon excited autofluorescence), to obtain biochemical and structural information on the remodeled ECM environment in asthma. METHODS: Non-transplantable donor lungs from asthmatic (n=13) and control (n=12) donors, were used for the assessment of airway collagen and elastin fibers by NLOM, and extraction of lung fibroblasts for in vitro experiments. MEASUREMENTS AND MAIN RESULTS: Fibrillar collagen is not only increased, but highly disorganized and fragmented within large and small asthmatic airways compared to controls, using NLOM imaging. Further, such structural alterations are present in pediatric and adult asthmatic donors, irrespective of fatal disease. In vitro studies demonstrated that asthmatic airway fibroblasts are deficient in their packaging of fibrillar collagen-I, and express less decorin, important for collagen fibril packaging. Packaging of collagen fibrils was found to be more disorganized in asthmatics airways compared to controls, using transmission electron microscopy. CONCLUSIONS: NLOM imaging enabled the structural assessment of the ECM, and the data suggest that airway remodeling in asthma involves the progressive accumulation of disorganized fibrillar collagen by airway fibroblasts. This study highlights the future potential clinical application of NLOM to assess airway remodeling in vivo