The circadian clock protein REVERBα inhibits pulmonary fibrosis development

Abstract

Pulmonary inflammatory responses lie under circadian control; however the importance of circadian mechanisms in fibrosis is not understood. Here, we identify a striking change to these mechanisms resulting in a gain of amplitude and lack of synchrony within pulmonary fibrotic tissue. These changes result from an infiltration of mesenchymal cells, an important cell type in the pathogenesis of pulmonary fibrosis. Mutation of the core clock protein REVERB in these cells exacerbated the development of bleomycin-induced fibrosis, whereas mutation of REVERB in club or myeloid cells had no effect on the bleomycin phenotype. Knockdown of REVERB revealed regulation of the poorly described transcription factor TBPL1. Both REVERB and TBPL1 altered integrin{beta}1 focal adhesion formation, resulting in increased myofibroblast activation. The translational importance of our findings was established through analysis of two human cohorts. In the UK Biobank circadian strain markers (sleep length, chronotype and shift work) are associated with pulmonary fibrosis making them novel risk factors. In a separate cohort REVERB expression was increased in human idiopathic pulmonary fibrosis (IPF) lung tissue. Pharmacological targeting of REVERB inhibited myofibroblast activation in IPF fibroblasts and collagen secretion in organotypic cultures from IPF patients, suggesting targeting REVERB could be a viable therapeutic approach.\n\nSignificanceThe circadian clock plays an essential role in energy metabolism, and inflammation. In contrast the importance of the clock in the pathogenesis of fibrosis remains poorly explored. This study describes a striking alteration in circadian biology during pulmonary fibrosis where the relatively arrhythmic alveolar structures gain circadian but desynchronous rhythmicity due to infiltration by fibroblasts. Disruption of the clock in these cells, which are not widely implicated in circadian pathophysiology, results in a pro-fibrotic phenotype. Translation of these findings in humans revealed previously unrecognised important circadian risk factors for pulmonary fibrosis (sleep length, chronotype and shift work). In addition, targeting REVERB repressed collagen secretion from human fibrotic lung tissue making this protein a promising therapeutic target.