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INTRODUCTION
Idiopathic pulmonary fibrosis (IPF) is a lung disease characterized by excessive remodelling of the extracellular matrix (ECM), where fibroblasts are one of the main producers of ECM components. Our aim is to understand how lung fibroblasts respond to mechanical cues in a healthy or diseased ECM composition. We have created an ex vivo model to mechanically stimulate fibroblasts repopulated in decellularized healthy or IPF lung tissue. We hypothesized that compositional ECM changes have an important impact on fibroblasts’ translation of mechanical cues from its microenvironment thus influencing disease progression.
METHODS
IPF and healthy distal lung tissue were decellularized in slices (350 um) to produce acellular lung scaffolds. The scaffolds were attached to a custom-made device for cyclic stretch built in polydimethylsiloxane and repopulated with healthy primary distal lung fibroblasts. The scaffolds were either exposed to cyclic stretch (0.2 Hz, 10% strain) or cultured under static conditions up to 3 days and analyzed for cell viability, histology, RNA expression and released mediators.
RESULTS
The secretion of VEGF-A in the IPF conditions showed a ~50% increase compared to healthy conditions for both conditions at 24h. Interestingly, at 72h the secretion of VEGF-A in IPF scaffolds decreased under cyclic stretch compared to fibroblasts cultured in healthy scaffolds where secretion increased. The IPF scaffolds had a higher VEGF-A secretion statically compared to heathy scaffolds whereas it was lower than the healthy when stretched. When looking at gene expression patterns of CTGF and CYR-61, fibroblasts in IPF static scaffolds had a higher gene expression of CTGF than in healthy scaffolds at 24h. Interestingly, the opposite trend was observed in cells cultured under cyclic stretch. The impact of ECM and mechanical stimulation was significant (P=0.0351) in altering gene expression levels of CTGF.
DISCUSSION
Our results indicate that the translation of mechanical cues is dependent on structural and compositional ECM organization. Secretion of angiogenic factors (VEGF-A) and expression of mechanotransduction factors (CTGF and CYR61) became altered primarily through the impact of cyclic stretch or ECM, respectively. These findings indicate that there is a synergetic interaction between mechanical stimulation and ECM that impact cellular responses in chronic lung diseases.
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