Advanced Image-Based Approach to Assess How Fibrillar Collagen Modulates Airway Reactivity

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 DESCRIPTION (provided by applicant): The airway smooth muscle (ASM) has traditionally been the focus of research into the etiology of airway hyperresponsiveness (AHR) in asthma. However, it is becoming increasingly clear that critical mechanisms leading to AHR cannot be gleaned by only understanding the ASM in isolation from its native environment. When the ASM cells constrict, their force/deformation has to propagate around the circumference of the airway in order for the airway to narrow. This is typically thought to occur through cell-cell contacts between ASM cells, with each ASM cell pulling on another ASM cell attempting to narrow the airway. However, in addition to the cell-cell interactions, it is well established that the ASM cels can form focal adhesions with the ECM. Therefore, it is possible that the ASM force can be transmitted around the airway wall through elements of the ECM such as fibrillar collagen that surround the ASM cells. A fundamental question that emerges from this line of thinking is: how does the ASM contraction in response to an agonist translate into the eventual narrowing of an airway and what role do the collagen fibers play, if any, in modulating airway caliber during the narrowing process. At present, it is impossible to address this question as nothing is known about what happens to the collagen fibers in the airway wall during a muscle contraction. Our proposal will advance an innovative and powerful approach that will use second harmonic generation (SHG) microscopy, a novel imaging technique, to link collagen fiber organization to stress transmission within the airway and consequently the response of airways. Our preliminary results indicate that SHG can be a viable technology to map out the changes in collagen fiber organization as a result of ASM activation or cyclic stretching. Further, when we exposed a freshly dissected airway segment to 10-5M acetylcholine (ACh) while imaging it real time using SHG, we found that counter intuitive to our present understanding of how an ASM force is transmitted around an airway, wavy collagen fibers at baseline appear to straighten in the post ACh image as the airway constricted. Such straightening is consistent with collagen fibers starting to carry tension when the airway is exposed to agonist and the ASM develops active force. If confirmed, this means that airway wall collagen plays a more direct role in transmitting force around the airway during an ASM contraction. Through this exploratory research proposal, we will provide the community with a quantitative understanding of changes in collagen organization caused by an ASM contraction or dynamic stretch and changes in airway wall stress that be mapped back to understand the process by which airways narrow.