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SRC family kinases modulate molecular pathways associated with mitochondrial dysfunction in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by a disturbed redox balance that can contribute to mitochondrial dysfunction. Mitochondria are critical for cellular homeostasis and when dysfunctional they can contribute to epithelial cell death. Recently, SRC family kinases (SFK) have been associated with IPF pathology although their exact role and activation in this disease are still unknown. In this study, we investigated whether SFK are activated in human bronchial epithelial (HBE) cells as well as in primary HBE cells derived from IPF patients and if SFK modulation interferes with molecular pathways controlling mitochondrial function. Here, we demonstrate that TGF-β1 can rapidly activate the SRC kinase FYN in HBE cells, which subsequently induces mitochondrial ROS (mtROS) production. Moreover, TGF-β1-induced FYN activation involves initial activation of NOX4 and direct oxidation of FYN. At the same time, both FYN and mtROS contribute to TGF-β-induced induction of NOX4. Interestingly, MitoQ pretreatment attenuated the TGF-β-induced increase in the mRNA expression of NOX4 and the profibrotic genes VIM and FN1 but not of COL1A1. In HBE cells derived from IPF patients, we found an increased SFK activation compared to that in control HBE cells which was reduced upon treatment with the SFK-inhibitor AZD. Additionally, this SFK inhibition in HBE cells from IPF patients increased the mitochondrial biogenesis markers NRF2, PGC-1β and ERRα and the mitophagy marker PINK1 which were originally decreased in HBE cells from IPF patients compared to control HBE cells. Collectively, these results indicate complex and reciprocal interactions between NOX4 and mtROS in TGF-β-induced profibrotic responses suggesting a role for SFK in mitochondrial dysfunction in IPF.