295 General discussion and future perspectives This combined approach to understand fibroblast responses that were dictated by the microenvironment to which they were exposed reflected the existing literature with respect to the instructiveness of the ECM in lung fibrosis [9, 13, 29, 34], and advanced it by providing an in vitro model system that recapitulated the biochemical and biomechanical complexity of lung ECM in vivo. The exaggerated responses of control fibroblasts might be explained by these fibroblasts being naïve and ready to be instructed by the microenvironment, while the IPF fibroblasts being already imprinted and less sensitive to the additional feedback coming from the hydrogels. In addition, I have shown how the fibroblasts responses differed with respect to parameters related to collagen fiber organization and mechanical properties of the hydrogels. While the initial efforts in understanding fibrotic ECM focused solely on the (accumulation of) collagens, there is now a growing body of evidence investigating the fiber organization, fiber crosslinking or ECM topography report how cells are able respond to structural arrangement of ECM alone [38-42]. These emerging studies could prove important especially for guiding new efforts to find novel therapeutic targets and develop new strategies to treat lung fibrosis by targeting not only fibrotic cells but fibrotic ECM characteristics. Building on the reports by Booth et al. [13] and Parker et al. [34], my results illustrate the capacity of fibrotic ECM-driven instructions through complex dynamics between the ECM and fibroblasts. An interesting observation from this study was that control fibroblasts changed the microenvironment even in control hydrogels, with respect to several parameters, which might indicate that these cells have an optimal set of conditions associated with their ideal environment and work towards establishing them. By understanding the de facto states of different cells within their microenvironment, future therapeutic strategies against lung fibrosis can be developed to target mechanisms that imbalance these default states. The mimicking capacity of the abovementioned model for capturing the lung microenvironment in vitro could be further bolstered by introducing another cell type such as epithelial cells to investigate interactions between different cell types and ECM (as reported in Chapter 5). Applying additional fiber crosslinking to separately investigate the influence of mechanical properties (as developed in Chapter 8) with the presence of fibrotic ECM composition could also advance the mimicry achieved in this model. Cell-seeded hydrogels derived from native human lung ECM brings a cutting edge to both basic and translational research. In conclusion, the findings of this thesis break new grounds in the field of fibrotic lung diseases. The new results and methods originating from this thesis provide new 10
RkJQdWJsaXNoZXIy MTk4NDMw