NISC-6

Radiation‐induced pulmonary fibrosis (RIPF) is a chronic, progressive, irreversible lung interstitial disease that develops after radiotherapy. Although several previous studies have focused on the mechanism of epithelial–mesenchymal transition (EMT) in lung epithelial cells, the essential factors involved in this process remain poorly understood. The DNA‐dependent protein kinase catalytic subunit (DNA‐PKcs) exhibits strong repair capacity when cells undergo radiation‐induced damage; whether DNA‐PKcs regulates EMT during RIPF remains unclear.

To investigate the role and molecular mechanism of DNA‐PKcs in RIPF and provide an important theoretical basis for utilising DNA‐PKcs‐targeted drugs for preventing RIPF.

DNA‐PKcs knockout (DPK−/−) mice were generated via the Cas9/sgRNA technique and subjected to whole chest ionizing radiation (IR) at a 20 Gy dose. Before whole chest IR, the mice were intragastrically administered the DNA‐PKcs‐targeted drug VND3207. Lung tissues were collected at 1 and 5 months after IR.

The expression of DNA‐PKcs is low in pulmonary fibrosis (PF) patients. DNA‐PKcs deficiency significantly exacerbated RIPF by promoting EMT in lung epithelial cells. Mechanistically, DNA‐PKcs deletion by shRNA or inhibitor NU7441 maintained the protein stability of Twist1. Furthermore, AKT1 mediated the interaction between DNA‐PKcs and Twist1. High Twist1 expression and EMT‐associated changes caused by DNA‐PKcs deletion were blocked by insulin‐like growth factor‐1 (IGF‐1), an AKT1 agonist. The radioprotective drug VND3207 prevented IR‐induced EMT and alleviated RIPF in mice by stimulating the kinase activity of DNA‐PKcs.

Our study clarified the critical role and mechanism of DNA‐PKcs in RIPF and showed that it could be a potential target for preventing RIPF.

Fibroblast growth factor 21 (FGF21) is expressed in several organs, including the liver, adipose tissue, and cardiovascular system, and plays an important role in cross-talk with other organs by binding to specific FGF receptors and their co-receptors. FGF21 represents a potential target for the treatment of obesity, type 2 diabetes mellitus, and non-alcoholic steatohepatitis (NASH). The production of FGF21 in skeletal muscle was recently suggested to be beneficial for metabolic health through its autocrine and paracrine effects. However, the regulatory mechanisms of FGF21 in skeletal muscle remain unclear. In the present study, we showed that berberine regulated FGF21 production in C2C12 myotubes in a dose-dependent manner. We also examined the effects of A-674563, a selective Akt1 inhibitor, on the berberine-mediated regulation of FGF21 expression in C2C12 myotubes. Berberine significantly increased the secretion of FGF21 in C2C12 myotubes, while A-674563 attenuated this effect. Moreover, a pre-treatment with A-674563 effectively suppressed berberine-induced increases in Bmal1 expression in C2C12 myotubes, indicating that the up-regulation of Bmal1 after the berberine treatment was dependent on Akt1. Additionally, berberine-induced increases in FGF21 secretion were significantly attenuated in C2C12 cells transfected with Bmal1 siRNA, indicating the contribution of the core clock transcription factor BMAL1 to Akt-regulated FGF21 in response to berberine. Collectively, these results indicate that berberine regulates the expression of FGF21 through the Akt1 pathway in C2C12 myotubes. Moreover, the core clock gene Bmal1 may participate in the control of the myokine FGF21. Berberine stimulated Akt1-dependent FGF21 expression in C2C12 myotubes. The up-regulation of FGF21 through the modulation of PI3K/AKT1/BMAL1 in response to berberine may be involved in the regulation of cellular function (such as Glut1 expression) by acting in an autocrine and/or paracrine manner in skeletal muscle.