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 REVERBα in these cells exacerbated the development of bleomycin-induced fibrosis, whereas mutation of REVERBα in club or myeloid cells had no effect on the bleomycin phenotype. Knockdown of REVERBα revealed regulation of the poorly described transcription factor TBPL1. Both REVERBα and TBPL1 altered integrinβ1 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 REVERBα expression was increased in human idiopathic pulmonary fibrosis (IPF) lung tissue. Pharmacological targeting of REVERBα inhibited myofibroblast activation in IPF fibroblasts and collagen secretion in organotypic cultures from IPF patients, suggesting targeting REVERBα could be a viable therapeutic approach.SignificanceThe 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 REVERBα repressed collagen secretion from human fibrotic lung tissue making this protein a promising therapeutic target.

Molecular clock REV-ERBα regulates cigarette smoke–induced pulmonary inflammation and epithelial-mesenchymal transition

“…We have shown that dysregulated EMT markers which are associated with REV-ERBα KO are mostly mesenchymal markers (Snail-Slug, Vimentin, COL1A1, and TGFβ), whereas epithelial markers showed the reduced expression between REV-ERBα KO and WT group. Our results, in part, highlight the important role of REV-ERBα in fibroblasts, these cells having a crucial role in exacerbating fibrotic responses in the lungs (17). The robust circadian gene oscillations in fibroblasts present the importance of circadian rhythmicity in fibroblasts and also has been shown to regulate the wound healing response in vitro and in vivo (32,33).…”

“…The dysregulated BMAL1 and CLOCK might be one of the reasons for EMT induced by CS, and the detailed mechanisms need further investigation. Interestingly, REV-ERBα has been associated with the pathogenesis of pulmonary fibrosis with possible an interaction with the transcription factor TBPL1 (17). We have shown that dysregulated EMT markers which are associated with REV-ERBα KO are mostly mesenchymal markers (Snail-Slug, Vimentin, COL1A1, and TGFβ), whereas epithelial markers showed the reduced expression between REV-ERBα KO and WT group.…”

“…We and others have reported that REV-ERBα agonists were capable of attenuating inflammatory responses (13,21,24). Recently, REV-ERBα agonists have been shown to modulate fibrotic responses in mice and ex-vivo human lung tissue (17). Additionally, SR9009 treatment in tendon fibroblasts showed a decrease in collagen fiber formation per cell, and CRY1/2 agonist: KL001, enhance the transcript levels of genes (Sec61a2, Mia3, Pde4d and Vps33b) that regulate collagen trafficking and fiber assembly, and the number of collagen fiber formation per cell (34).…”

“…In a different loop, RORs compete with REV-ERBα/β for binding with ROR response elements (RORE), with RORs contributing to the activation of BMAL1 transcription, whereas REV-ERBα/β inhibits it (12). Previous studies have shown that circadian clock molecules play an important role in the pathogenesis of chronic lung diseases, such as pulmonary fibrosis, COPD, and even lung cancer (13,(16)(17)(18).…”

Recent advancements in pulmonary arterial hypertension and right heart failure research: overview of selected abstracts from ATS2020 and emerging COVID‐19 research

“…The circadian clock plays an essential role in many aspects of behavior and physiology, including sleep/wake cycles, regulations of blood pressure and body temperature, energy metabolism, and inflammation. 49,50 Disrupted circadian rhythms of lung function and inflammatory responses have been implicated in pulmonary fibrosis, COPD, asthma, and inflammation [51][52][53] ; however, the role of the molecular clock and the impact of circadian disruption in the pathogenesis of PAH remain poorly explored. The circadian clock consists of a positive arm -CLOCK and BMAL1 heterodimers, which drive transcription of two inhibitory arms -PER/CRY and REV-ERBa/REV-ERBb (also known as NR1D1 and NR1D2).…”