In animal experiments, metformin was reported to not only mitigate bleomycin- and radiation-induced lung injury and pulmonary fibrosis through the activation of AMPK (Choi et al., 2016; Azmoonfar et al., 2018; Farhood et al., 2019; Xiao et al., 2020), but also protect against fine particulate matter (PM2.5, aerodynamic diameter≤ 2.5 μm)-induced lung injury and fibrosis through AMPK independent pathway (Gao et al., 2020). The gene discussed is PRKAA1; the disease is fibrosis.