Activation of Fibroblast LRP1 by AT2-secreted MDK Affects OTUB1/SLC7A11 Ubiquitination to Inhibit Fibroblast Ferroptosis in Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF), a chronic interstitial fibrosing pneumonia of unknown cause, is characterized by an irreversible decrease in alveolar cells and an increase in fibroblasts. In our research, the numbers of AT2 cells and fibroblasts are abnormally regulated, but AT1 cells are significantly reduced in lung tissue sections from patients with IPF and mice. By analyzing the single-cell sequence from GEO database and experimental validation both in vivo and in vitro, it is found that the abnormally regulated AT2 cells secreting a large amount of MDK to activate the CTHRC1+ fibroblasts LRP1 receptor and inhibit the ferroptosis of fibroblasts. Further, by activating the LRP1 receptor in CTHRC1+ fibroblasts, the RNA-seq results reveal that the expression level of OTUB1 increased significantly. The ubiquitination experiment results showed that OTUB1, as a deubiquitinated molecule, can directly bind to the ferroptosis inhibitory protein SLC7A11, removing the ubiquitination modification of SLC7A11 and stabilizing its expression level to inhibit ferroptosis in fibroblasts. Meanwhile, this molecular pathway was verified in mice by dropping adenovirus through the airway, and the same experimental results as in vitro were verified. In conclusion, our study verified that IPF leads to abnormal regulation of AT2 secreting MDK, which activates LRP1 receptor and increases OTUB1 in fibroblasts. Deubiquitylation modification of OTUB1 stabilizes the expression level of SLC7A11, which results in a decrease in fibroblast ferroptosis, leading to an abnormal regulation of its programmed death, ultimately the deterioration of IPF.