title: The Role of OGG1-Mediated DNA Damage Signaling in Circadian Regulation of Pulmonary Cell Homeostasis: Implication for Chronic Lung Diseases
Creators: name: Al Duhneen, Abdulhadi
Publisher: name: University of Liverpool Repository
Year: 2024

description: Circadian rhythm disturbances have emerged as crucial factors underlying cellular dysfunction, compromised DNA repair mechanisms, and the development of a spectrum of chronic disorders, including lung diseases. While existing research has underscored the dependency of OGG1 activity on circadian timing, it remains unclear whether a malfunctioning circadian clock plays a pivotal role in the dysfunctional OGG1-BER signaling observed in chronic lung illnesses. 

Furthermore, the pro-inflammatory cytokine, TNF, is known to exert a pivotal role in the pathogenesis of various inflammatory conditions, attracting inflammatory cells, fueling the production of inflammatory mediators, enhancing oxidative stress, and triggering airway hyperresponsiveness. In this study, TNF stimulation was employed in human lung epithelial cell cultures (BEAS-2B and A549) to investigate the intricate relationship between DNA repair enzymes (Ogg1) and clock genes (Bmal1, Cry1, Per2, and NR1D1). Through the utilization of serum shock to synchronize the circadian clocks in both lung cell lines, we unequivocally establish that BEAS-2B and A549 cells conform to circadian cycles. Evidence suggests that OGG1 mRNA expression is intricately regulated by circadian time shifts in normal lung epithelial cells (BEAS-2B), where it oscillates in phase with the clock gene Per2 and antiphase with the clock gene Bmal1. Conversely, cancer lung epithelium (A549) exhibited an opposite pattern. Comparing A549 to BEAS-2B, it becomes evident that A549 displays an augmented amplitude of clock gene expression alongside a diminished OGG1 mRNA level. Intriguingly, silencing OGG1 with small interfering RNAs (siRNAs) leads to an upregulation of clock genes BMAL1 and NR1D1 in both cell lines. Furthermore, our findings indicate that OGG1 functions as a suppressor of pro-inflammatory cytokines in normal lung epithelial cells, but the inverse holds true for lung cancer. 

Preliminary investigations using the inflammatory stimulus TNF reveal that a concentration of 10 ng/ml is potent enough to trigger inflammation and modulate clock genes (Bmal1 and NR1D1). At the peak of NR1D1 expression, interleukin-6 and interleukin-8 levels decline in BEAS-2B, while A549 shows variable patterns at different times of the day. Notably, siRNA knockdown of Cry1 results in the downregulation of multiple OGG1 isoforms at the mRNA level, reinforcing the hypothesis of an intertwined function between OGG1 and the circadian clock in chronic pulmonary diseases.Comparatively, BEAS-2B cells demonstrate enhanced resilience to inflammatory stimuli when contrasted with A549 cancer cells, corroborating the proposed model of the inflammatory process. Within human lung epithelial cells, the DNA repair protein OGG1 is favorably regulated by Cry1. 

Lastly, the dynamic assessment of core clock gene expression, particularly Bmal1, in human lung epithelial cells was made possible through the development of two novel clock reporter cell lines stably transfected with the Bmal1::Luc clock reporter gene in BEAS-2B and A549. This research sheds light on the intricate interplay between circadian rhythms, DNA repair, and inflammation in lung diseases, offering valuable insights for future therapeutic interventions.