Role of Mitochondrial Metabolism in Phenotypic Plasticity of Lung Fibroblasts

Introduction: Differentiation of fibroblasts into myofibroblasts is an important stage in fibroproliferative reaction. However, deregulation of differentiation and excessive accumulation of myofibroblasts can cause hypertrophic scar formation and fibrosis in lung tissue. The goal of this study is to investigate the role of mitochondrial metabolism in signaling, modulation of cytoskeleton and fibroblast activation. The specific objects are to investigate the role of mitochondrial metabolism in fibroblast phenotypic plasticity in vitro and in further studies in the fibroproliferative response after bleomycin treatment in vivo.

Methods and Results: Here we demonstrate that murine primary lung fibroblasts, stimulated with the profibrotic cytokine transforming growth factor-β (TGF-β), sow an increase of the resting mitochondrial membrane potential. Interestingly, these cells with the high mitochondrial membrane potential, demonstrate increased proliferation, migration and profibrotic phenotype. Furthermore, investigating mitochondrial fusion and fission processes show, that the profibrotic phenotype of these murine lung fibroblast is accompanied with enhanced mitochondrial fusion processes. Moreover, murine primary lung fibroblasts, sorted for low and high resting mitochondrial membrane potential (ΔΨ_m ^low and ΔΨ_m ^high) are indistinguishable morphologically. In contrast, ΔΨ_m ^low cells demonstrate reduced expression of fibrotic markers like alpha-smooth muscle actin, collagen 1, or fibronectin, compared to ΔΨ_m ^high murine lung fibroblasts, using immunofluorescence, western blot and qPCR analysis. Interestingly, the phenotype of primary murine lung fibroblasts sorted for ΔΨ_m ^low and ΔΨ_m ^high is stable can be observed up to 10d after cell sorting. Finally, sorted murine lung fibroblasts demonstrate increased mitochondrial fusion processes, which are associated with a profibrotic phenotype of these cells.

Discussion/Outlook: Our data suggest that the mitochondrial metabolism plays an important role in the phenotypic activation and proliferation of lung fibroblasts. Furthermore, a coupling between intrinsic metabolic parameters and fibroblast fate might form a basis for novel therapeutic options.