Tetrahydrobiopterin metabolism attenuates ROS generation and radiosensitivity through LDHA S-nitrosylation: novel insight into radiogenic lung injury

Genotoxic therapy triggers reactive oxygen species (ROS) production and oxidative tissue injury. S-nitrosylation is a selective and reversible posttranslational modification of protein thiols by nitric oxide (NO), and 5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for NO synthesis. However, the mechanism by which BH4 affects protein S-nitrosylation and ROS generation has not been determined. Here, we showed that ionizing radiation disrupted the structural integrity of BH4 and downregulated GTP cyclohydrolase I (GCH1), which is the rate-limiting enzyme in BH4 biosynthesis, resulting in deficiency in overall protein S-nitrosylation. GCH1-mediated BH4 synthesis significantly reduced radiation-induced ROS production and fueled the global protein S-nitrosylation that was disrupted by radiation. Likewise, GCH1 overexpression or the administration of exogenous BH4 protected against radiation-induced oxidative injury in vitro and in vivo. Conditional pulmonary Gch1 knockout in mice (Gch1fl/fl; Sftpa1-Cre+/− mice) aggravated lung injury following irradiation, whereas Gch1 knock-in mice (Gch1lsl/lsl; Sftpa1-Cre+/− mice) exhibited attenuated radiation-induced pulmonary toxicity. Mechanistically, lactate dehydrogenase (LDHA) mediated ROS generation downstream of the BH4/NO axis, as determined by iodoacetyl tandem mass tag (iodoTMT)-based protein quantification. Notably, S-nitrosylation of LDHA at Cys163 and Cys293 was regulated by BH4 availability and could restrict ROS generation. The loss of S-nitrosylation in LDHA after irradiation increased radiosensitivity. Overall, the results of the present study showed that GCH1-mediated BH4 biosynthesis played a key role in the ROS cascade and radiosensitivity through LDHA S-nitrosylation, identifying novel therapeutic strategies for the treatment of radiation-induced lung injury. Radiation therapy for cancer can harm healthy tissues, causing swelling and oxidative stress (an imbalance between free radicals and antioxidants in your body). This research examined the part of a molecule named tetrahydrobiopterin (BH4) in this. The scientists discovered that radiation therapy decreases the amount of BH4 in the body, which then leads to a rise in harmful reactive oxygen species (ROS - molecules that can damage cells). However, when BH4 amounts were artificially boosted, this lowered ROS levels and shielded against radiation-caused harm. This implies that BH4 might be used as a treatment to guard against the damaging side effects of radiation therapy. More research is required to further investigate this potential in clinic. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.