Platelets and airway remodeling Mechanisms involved in platelet-induced fibroblast and airway smooth muscle cell proliferation in vitro

Airway remodeling is a contributing cause to the pathological structural changes, such as increased cell proliferation, observed in asthma. Platelets have been found in autopsy lungmaterial obtained from asthmatic patients and are well known to induce proliferation in vitro of a variety of cells. However, the role of platelets in airway remodeling is far from understood. This thesis aims to clarify the involvement of platelets in fibroblast and airway smooth muscle cell (ASMC) proliferation in vitro and to elucidate the importance of HA, FAK, eicosanoid and ROS dependent signaling. The results demonstrate that platelets induce ASMC proliferation through NADPH-oxidase and 5-LOX dependent mechanisms. In addition, platelets induce a 5-LOX dependent fibroblast proliferation. Morphological analysis suggests that platelets bind to the extracellular matrix component HA through its receptor CD44 and thereby induce a FAK dependent ASMC proliferation. Taken together, the results obtained in this thesis suggest that platelet/HA interaction mediated through CD44 is of importance for platelets ability to induce cell proliferation. Moreover, the results propose that platelet-induced fibroblast proliferation is 5LOX dependent and that platelets induce a HA, CD44, FAK, 5-LOX, and ROSmediated ASMC proliferation. This action of platelets represents a potential important and novel mechanism that may have an impact on the remodeling process and in the development of new pharmacological strategies in the treatment of inflammatory respiratory disease such as asthma.